An organ (especially a pipe organ in a church) is the most expensive instrument in the world, I saw some even cost in the millions of dollars. I've read a lot of mixed things about weighted/unweighted keys but the general consensus, at least in the realm of keyboard synths/controllers is people consider weighted keys to feel more "premium" and consequently they cost more too. So I was wondering why doesn't the most expensive instrument have weighted keys?
The main point of weighted keys are that they give more feel for the dynamic response of a piano-like instrument. Specifically, weighted keys make it so that gentle playing only results in gentle velo, i.e. low dynamic level. To play forte on a weighted keyboard, you literally need to put in some force, and that makes sense for the performance. With an unweighted keyboard, the force-dynamic relationship is much harder to control.
But: an organ doesn't have dynamics (or rather, the dynamic level isn't controlled by key velocity but by registration, volume pedal etc.), so it's moot.
However, pipe organs do have their own kind of “weight” on the keys, namely the pressure needed to overcome the valve resistance. This is quite different to weighted piano action though. See guest's answer for details.
A so-called "tracker action" organ keyboard, where there is a direct mechanical connection between the key and the valve that lets air into the pipes to play the notes, has a very distinctive feel that is completely different from a piano "hammer action" and from the "dead" feel of a cheap spring-loaded keyboard.
The force to start pressing the key down is high, but as soon as the air valve is cracked open the key force decreases. This has the double advantage that the initial high resistance tends to reduce "wrong notes" when your fingers mis-hit the keys, but the effort to hold down long notes is reduced. Compared with piano playing, you often need to hold down a long note with one finger (or thumb) while playing other shorter notes with the same hand.
In good quality large instruments which do not have this direct connection between the keyboard and the pipes, the keyboards are designed to have the same "feel" as a real tracker-organ keyboard, not a piano keyboard.
Most organs have more than one keyboard, and it is a standard technique to play notes on two keyboards at the same time with one hand, usually with the thumb playing notes on one keyboard and the fingers on the one above it. This is a completely different hand and arm position than piano playing.
Since large organs may have four or five (or even more) keyboards, the position of each keyboard relative to the player is different, and the two hands are often playing on different keyboards. Again this results in very different hand and arm playing position than for a piano.
In other words, just because pianos and organs both have "keyboards" the actual playing techniques are quite different, and there are good reasons why the "feel" of the keyboards is different.
A piano doesn't have weighted keys to "feel premium", but because the hammer is part of how the piano works.
The hammer isn't part of how an organ works, so it doesn't have weighted keys.
the general consensus is people consider weighted keys to feel more "premium"
If you're talking about a keyboard to trigger a piano or piano-like sound, there's probably a consensus, as it makes for a better imitation of a real piano. I doubt there's a consensus that a weighted keyboard makes for a better organ-playing experience.
Organs are not "expressive" keyboard instruments. In other words the volume of a key press on an organ isn't dependent on how hard you press the key like it is on a piano. Organ keys are only "on" or "off". Volume is controlled separately (usually by a pedal or other control) and all keys will have the same volume based on that setting. Key weighting on electric pianos is intended to mimic the hammer action of a mechanical action piano. The action of these mechanical hammers is what gives "real" pianos their expression when you push the key hard or soft. Electronic pianos use a sensor to determine how hard you hit the key and don't require the weighting to produce this sensation. "Premium" weighting on keyboards just makes the keys "feel" like a "real" piano, where the sensor responds to the weighting mechanism instead of the pressure on the key itself. Since an organ doesn't have any "expressive" feedback, it wouldn't make any sense to offer a weighted action because the action wouldn't "do" anything. That being said higher end organs will have a more consistent and "robust" feeling spring return to the keys vs. a low quality organ, but organ keyboards have never been made with the intention of feeling like a piano.
The previous answers thoroughly cover the differences in organ vs. piano mechanics, but I'll add one small point of consideration when discussing modern electronic keyboards and the pros/cons of (what I learned to call) "weighted" vs. "synth" action designs. While weighted keys would likely be preferable to anyone accustomed to playing a "real" piano, they do come at the cost of added instrument weight. And that becomes a negative, if that electronic instrument is going to be lugged around and set up in clubs, halls, bars, etc.
Weighted keys on an electric piano certainly are a selling point and cost more. But there is a practical reason. The weight provides some resistance and that resistance help you gauge how much velocity you put into the keys with your fingers. It sort of feels like an acoustic piano keyboard action, but it isn't the same mechanically, and in my opinion they don't feel exactly the same. Whatever the case, there is a practical point to weighted electric piano keys.
The other answers already point out that organs don't (as far as I know) have weighted keys, because there is no touch sensitivity, volume control in the keys.
Most of the electronic pianos I have seen (with weighted keys) also have settings for organ and harpsichord and key velocity can change the volume of those sounds. Also, the key size on real organs and harpsichords is much smaller than modern full sized keyboards.
A really versatile and experience keyboardist probably knows the different feel of these various instruments old and modern. But for someone who plays organ, harpsichord, clavichord on a modern, full sized, weighted electric keyboard and then tries the real instrument, the difference will probably be a surprise.
Organs don't have weighted keys because of two facts. First, weighted keys are supposed to make keyboards feel more like pianos. Second, organs were invented a thousand years or more before pianos. Organs and organists had centuries to develop ideal organ actions and playing techniques adapted to those actions before the piano began to be developed.
Modern organs have not begun using weighted keys in their keyboard because existing organ repertoire would be ill suited to such a keyboard. It was designed to be played on an organ keyboard.
A weighted keyboard is a relatively recent development which attempts to replicate the feel of a good old fashioned hammer action acoustic piano (which did not actually have weighted keyboards). The only reason they even exist is to try to duplicate that original feeling when playing an electronic keyboard. It is more expensive to manufacture a keyboard with weighted action, so the cost increases for the customer, leading to the premium classification in a lot of folks minds. Weighted keyboards were developed for use on portable keyboards. I personally am not familiar with the existence of any portable pipe organs, so I don't think any modern day engineers or designers have ever even considered the use of weighted keyboards in their products. As a point of distinction, I'm assuming you are asking specifically about actual pipe organs, as opposed to the sound of a pipe organ program often included in a synthesizer package.