At point of purchase, you get to decide whether you want secure mode or not. Then after that, if you want to change it, you have to open a support ticket with the manufacturer.
Kinda like how SIM-locking works.
If they can be convinced of that, how hard will it be for a scammer to say "we've detected a problem with your phone. To avoid being imprisoned for piracy, please file this support ticket so we can debug things."?
Making the device so locked down that no such con could exist also means there's no way to use the phone in ways that haven't been authorized - and as a power user, i detest that i am paying a price for the safety of those who are too stupid. I do not want to pay that price.
Conveniently, google gets to remain in a position to earn more money from being in the controlling seat.
as they say, if you trade freedom for security, you'll end up with neither.