USB Mass Storage never caused me any issues. I absolutely refuse to 'adapt' to MTP. That's why I rock so many old Androids. I prefer ease and convenience over whatever asinine thing Google wants us to do. The SD card in my phone is FAT32 but since USB Mass Storage is gone, can't even mount that on PC easily. Much less use it to play media via the aux USB input on my infotainment system in vehicles. They just don't see the music on modern phones.
My car is old enough it doesn't have USB input in the first place, so that's not a problem for me
.
I've not even had a microSD slot for most of a decade, but I have a couple of USB microSD readers, so would just use one of those for a computer. But I have no problem transferring files over USB to a phone, so can't say I found UMS easier or more convenient. To me the only differences are that I can still use the phone while doing so (if I want to, which I usually don't) and that I know there's no point trying to use file recovery software over MTP. It's also faster, but that's probably just down to newer USB hardware in both phone and computer.
Remember when android was all about choice? Since when is it ok to copy Apple and lock everything down to save some idiots? Where's the revolt that would have happened had they tried this in 2011? Even this forum wouldn't have been so tolerant of Google's decisions lately.
Actually there was no revolt here when they switched from UMS to MTP that I recall. And absolutely nobody wanted the old system of fixed "data" and "sdcard" partitions in their internal storage: although some of us complained (and still do) about Google hanging onto misleading legacy names like "sdcard" for virtual volumes, which would confuse people who didn't understand how the filesystem actually works, I remember everybody finding being able to fill the internal storage with whatever mix of apps, data or media you wanted, rather than running out of one kind of space while having the other partition half empty, a great improvement. And as Mike said above, that change was not compatible with keeping UMS and letting Windows users transfer files via USB at all (since Windows didn't understand linux filesystems), so for most people any minor inconvenience from MTP was a price worth paying.
I have plenty of problems with Google (I trust them slightly more than Facebook, but that's about it), but the switch of filesystems, which is what lay behind the abandoning of UMS, is not one of them.
Of course it would have been possible to keep UMS as an option for microSD cards, but by that point Google had long ago lost interest in those anyway (the last Google device with a microSD slot was the Nexus One in 2010), so it's no surprise that they didn't include separate provision using a different access method for those.
