[jimmySixDOF]

To be fair Android as in ASOP is truly FOSS but because all drivers are baked into the kernel for reasons better lost to the sands of time, Vendor/Carrier pairs can enforce what they like in their required custom builds. This is what Google's project Fushia was/is supposed to solve.

[phonedog]

Not since Project Treble they're not.

The more pressing issue is that bootloader unlocking isn't as ubiquitous as one might like.

[jimmySixDOF]

It could also be said that being able to re-lock after cooking your ROM is just as important and even more missing