The fact that many Android bootloaders are not allowed to be unlocked by users means, by definition, these devices were never yours to begin with. It is not Google taking away your ability to use your sideloaded apps on your device because true, unlimited device freedom was never yours to begin with.
Hence my phone selection spreadsheet having a column for unlockability, making sure I don't forget to check it. I'm so used to root, I'd full-on buy the phone just assuming it's a thing when some vendors indeed block you
That this is now rolled out ecosystem-wide by the central controlling party is a significant change from some vendors being assholes