The guitar tuning (switch from perfect 4ths to a major third) makes sense when you are playing 4+ strings simultaneously. I read a study a while back that someone even ran some kind of computer program to determine if there was a more efficient way to tune a guitar, given the purpose and physical ability of the human hand, and it said the standard tuning was actually the most efficient way to make it work.
Of course, most bass players are not playing 4+ strings at once, and as such, the instrument doesn't need to be tuned to make that an efficient thing to do. Since the bass is already in perfect 4ths it makes sense to keep all strings that way, which makes all of your shapes and modes symmetrical and linear. Given that a bass player might reasonably play 2 or 3 strings at once, but much less often 4 (save for tapping, which would be a different tuning question entirely) it makes the most sense to maintain perfect 4ths tuning so those shapes are in alignment.
Of course, most bass players are not playing 4+ strings at once, and as such, the instrument doesn't need to be tuned to make that an efficient thing to do. Since the bass is already in perfect 4ths it makes sense to keep all strings that way, which makes all of your shapes and modes symmetrical and linear. Given that a bass player might reasonably play 2 or 3 strings at once, but much less often 4 (save for tapping, which would be a different tuning question entirely) it makes the most sense to maintain perfect 4ths tuning so those shapes are in alignment.
