For decades there has been endless policy wrangling over whether “unlocking your phone” (removing restrictions allowing you to take the device with you to another carrier) should be allowed. Giant carriers have generally supported onerous phone locks because it hampers competition by making it harder to switch providers. Consumer rights groups and the public broadly support unlocked devices.
It’s been a number of years since I last regularly worked in cell phone repair, but some models of phones were physically made in different varieties with different antennas for different networks.
It wasn’t even possible to ‘unlock’ those phones for other networks, short of replacing the logic board and antennas.
Phones are also small computers, and while its wireless chipset may only be compatible with certain carriers, that doesn’t mean that I shouldn’t be allowed to install whatever I want on it.