I think it's reasonable for Google to control what happens in their version of Android (which can be installed by default) but it's not reasonable for Google to lock the bootloader (preventing installation of a non-Google OS).

Perhaps this is why Google hardware doesn't have locked bootloaders; Samsung et al can get away with locked bootloaders since it's not Google forcing the consumer in that case.

Whether the bootloader is or isn't locked should be very conspicuous before purchase, for consumer protection.