Is it not possible to buy a phone in the US without any cellular providers involved? I thought that kind of lock-in was a thing of the past.
This is separate from SIM locking, which forbids use with another carrier. US carriers still do that, but are required to remove the lock after a while if the customer doesn't owe them money.
It's not clear why Verizon insists on permanently locked bootloaders or why Google agrees to it for Verizon when they don't do it on Pixels sold anywhere else.