Since we're listing our own hypothesis, here's mine with some overlap.
1)There are more jazz makes than there are classical makes and there are more models and variations in the jazz makes than there are in the classical makes. There are enough options in jazz pieces that (if you have the resources) you're bound to find something that gives you what you're looking for.
2)There are more custom makers for jazz mouthpieces. (Is there a custom classical maker?)
3)The spectrum of good jazz tones is larger than the spectrum of good classical tones. With classical tone, there's a general consensus of how it should sound and you have to find a piece that allows you to sound that way. There are so many acceptable tones in jazz that you can sound great even if you don't quite have the the tone you're aiming for.
For me personally, I'm a jazz guy. I spend more time on my jazz setup and naturally have a more developed sound with it. Also, since I'm hardly ever in a classical setting, I have no inclination to try mouthpiece after mouthpiece in search of what works best for me.