Well, it has something to do with it. In the context of Pixels, carrier‐unlocked phones always allow the bootloader to be unlocked, Verizon‐locked phones never do (see, e.g., https://discuss.grapheneos.org/d/24254-no-way-to-use-my-veri...), and for other carriers it varies but often requires additional manual fiddling. To quote the GrapheneOS FAQ:

> Devices sold in partnership with specific carriers may be locked by the carrier, which will prevent installing GrapheneOS. This is primarily an issue with US carriers and isn't common elsewhere in the world. To avoid this, either don't buy a carrier device, or make sure it can be unlocked.