I think it has to do with cost saving and simplified support ... it's easier to relate to just the latest version ... versus having to take into account different releases of the OS. I think this is one of the main reason why so many hardware/software manufacturers have dropped support for XP. It's a cost saving decision and will in the end force an upgrade from win7 to the next "wonder". My suspects are not in the programming department, but the smart asses in the business lounge.
I think there are empirical test that show that there is little to nothing to be gained from 64- vs 32-bit computing, I can't recall sources at the moment ... but I think some performance tests for windows actually showed "au contrair". It actually went slower with 64 bit, this was explained away with how there where bug in code which was different for 64 bit. I don't know. My main audio machine at the moment is an win7 x64 ... but I only use the 32 bit versions of programs on it. Works good for me. Avoids a lot of trouble for nothing.
I guess win7 is approaching the end of it's life time, and I have a machine running win10 ... it's not to bad by MS standards ... they seem to manage a decent OS every other time ... but I fail to see any reason to upgrade except by force. It's hard to imagine now exactly what may be that force from a audio perspective, but someone really would need to come up with some revolutionary new touch screen based app ... and I fail to imagine how they are gonna beat apple on that front. There is no way that it will be some new cheap plastic usb controller ... I'm all stocked up in that department ... and have gone retro