I got significantly better performance for live processing (Guitar amp and effects VSTs) in 64bit Live when I still had an i5/4GB RAM system, especially at higher sample rates (96kHz). Something like 25% better, meaning setups I could run at 64bit couldn't be run in 32bit without choking. But if you're not having issues right now, why switch? Ableton for one recommends you stay with 32bit.
Other than that I'm with what Ryan0751 said. 32bit is over, and Live was probably the last demographically significant 32bit bastion to fall. Live is also the only DAW I've used that's been all prissy about 64bit. First it's "you don't need 64bit, it's just for tech snobs", now suddenly it's "you don't need a native bit-bridge, in a few years nobody will have 32bit anyway. But wait, when in doubt, use our old 32bit executable."
That's probably because with the release of Live 9, and Push, they didn't have enough engineering resources to properly test their 64-bit version.
Therefore they are trying to mitigate risk and defect count
This kind of thing is done all the time. Software is an inherently complex beast, particularly something like Live. The amount of code must be insane, and it's a fairly small team.