Surely some of that kind of thing would come down to regulatory compliance like emissions? It would be no good if right beside the BMW dealer was a shack with a dude who "unlocks" your new car's performance by turning it into a soot-spewing disaster (yes I know about coal rolling, but at least right now that's mostly done for jackass reasons not performance reasons).
Anyway, it's basically the same thing that's at stake with router radio firmware and RF compliance— yes, you own the device, but the device's hardware has inherent capabilities that if fully unlocked, you would really need additional permits/licensing/oversight to operate in a way that doesn't interfere with other people's devices and wellbeing. Having your device locked down in this regard is a compromise that lets you have it and use it within those parameters while not needing to become a domain expert.
Anyway, it's basically the same thing that's at stake with router radio firmware and RF compliance— yes, you own the device, but the device's hardware has inherent capabilities that if fully unlocked, you would really need additional permits/licensing/oversight to operate in a way that doesn't interfere with other people's devices and wellbeing. Having your device locked down in this regard is a compromise that lets you have it and use it within those parameters while not needing to become a domain expert.