Very interesting topic IMHO!
I don't think it can be generalized by saying that all people with personality x are likely to play bass more than personality y. On the other hand, I like to believe that it does take a particular kind of personality to want to play bass, i.e. maybe more mellow, background-dwelling, etc.
That being said, I think a big influence is what kind of music you grew up with. If you mainly listened to funk, disco, soul (i.e. bass heavy music) or rock, metal (guitar heavy music), chances are that might have steered you in a certain direction. But I listened to Led Zep, Jimi Hendrix, Nirvana, RHCP and I still wound up playing bass (after 14 years of guitar, that is).
Maybe, I just throwing ideas around, your hearing could also be a big factor. If you're sensitive to certain frequencies, like treble hurts your ears, bass makes you need to poop, etc., but find other frequencies more pleasing, that could also steer you towards a certain instrument.