The following answer pertains to diatonic harmonicas, a.k.a. blues harmonicas.
All the draw bends are produced by the same (two) principle(s).
To understand why the holes behave differently, it helps to understand how bends work. I quote my own answer to the linked question:
The sound of a harmonica is produced by reeds mounted over reed
slots. When air flows over the reed and pulls it into and through
the slot, it starts to vibrate and a tone sounds. Each hole has two
reeds, one mounted on the outside and one mounted on the inside.
During normal play, the inside reed sounds when you blow, pushing it
into its slot, and the outside reed sounds when you draw, sucking it
into the slot.
A harmonica reed can, however, also be made to sound with air
travelling in reverse, pulling the reed out of the sot instead, which
produces a note about one half step sharper that produced in normal
play.
Additionally, the tone of each reed is somewhat flexible, and can be
changed somewhat away from its natural frequency by the player.
You can see these effects for yourself by removing the cover plates of your harmonica and cover the slot of one of the reeds with a finger!
First cover the blow reed.
With only the draw reed available, you will note that it doesn't matter much which hole you choose, even the top octave behaves the same:
you can still bend the draw note a little bit, but it's hard to produce stable bends that are in tune. This is the same kind of bends that are available on chromatic harmonicas, heavily employed by players like Stevie Wonder and others.
In holes 1 through 6, the draw reed is tuned higher than the blow reed. When you start to draw bend a note, this is the first effect that comes in.
Now, cover the slot of the draw reed.
This might be trickier, but if you try to draw bend you might find a tone roughly one half step sharper than the blow note! By subtly changing the shape of your mouth, you might find that you can move this note around a bit.
When you play a draw bend, both these effects are in play!
If you draw without bending, only the draw reed sounds. As you start to bend, most of the sound still comes from the draw reed, which behaves in the same way as if the blow reed had been covered. As you go further down, the working-in-reverse blow reed comes into action and will eventually dominate the sound.
Because there is a strong resonance about half a step above the blow reed, it's hard ( if not impossible) to bend further. This explains the pattern of which bends are available, and can be summarised as follows:
In every hole, the higher note can be bent down to about one half step above the lower note.
In holes 2 and 3, there's a lot of space for the two effects to interact. This means large bends, but requires more precision.
In holes 1, 4 and 6, the blow and draw reeds are close enough in pitch that they can both sound strongly at the note in between, and these are the easiest bends, both to produce and to control.
In hole 5, if you try to bend you might get the blow reed working in reverse, but since this is already at the pitch of the draw reed you don't get any further.
As a bonus, this theory also explains overblows, also indicated in your table! If you cover one of the blow reeds (you might have to try different ones to find the best set-up hole!) and you try to blow bend, you get what is called an overblow, one half step above the draw note. With practice (and a good harmonica!) you can get this note sounding without covering the blow reed with your finger. When you learn this, the harmonica becomes a completely chromatic instrument, in theory able to play any tune in any key!
