The difference is that guitar technology is hopelessly stuck in the 50s, whereas bass technology has moved on to actually make use of what was available in... the 80s or so.
Namely, these basses with many knobs use active circuitry, which means you can tweak the frequency response as you wish – or leave it completely neutral. By contrast, the passive electronics that are found in almost all electric guitars (and a lot of basses, to be fair) are always colouring the sound in the extremely crude, hardly controllable way which is what you get from the simple filter character created by the PUs' inductance plus cable capacitance plus passive pots&tone-cap.
“But that extremely crude sound is all we want”, the guitarists will say. Well, except it's not, they will tweak the heck out of it with all kinds of pedals. That's of course still an option you have on bass as well, but why not include the essentials right there in the instrument, where you can fine-tune anything at any time without going to the amp or kneeling down to the pedal board?
It's particularly useful when you're arriving to a small festival where there's some bass amp on stage the bands are sharing, you can just plug in and dial in the sound from your own instrument, rather than needing to fiddle with the dials on that unknown amp.
(Well, in theory... in practice it usually turns out that the amp has, like, all the mids completely pulled, and at that point there's only so much an EQ in the instrument can do...)
It also has to do with how guitarists and bassists approach sound changes. Guitarists often switch between dramatically different sounds in the sections of a single song. That's best done by switching an effects pedal or amp-channel, or possibly to a different pickup.
On bass, you'll more typically run broadly the same sound throughout, and only fine-adjust to fit the dynamic context. And these adjustments may be quite different depending on room acoustics, placement on stage, what kit the drummer is playing on etc. etc., so they can hardly be pre-programmed into stomp boxes.
Finally, as was commented in other places in this thread, guitarists seem to have more of a problem with accidentally moving the pots on their instrument. Well, that's not all that surprising – first, guitarists simply tend to move more than bassists (there are of course exceptions), bassists tend to pluck more than they strum, which keeps the hand away from the pots, and even when they use a pick the palm usually stays anchored somewhere over the strings or bridge, whereas guitarists may well strum all over the instrument.