They can, it would likely just increase the cost of cheap devices to end users, as the manufacturer now has to provide additional software support and does not want to lose money.
I never had to wait on Dell to type apt update and apt upgrade.
You've never had to wait for Dell to type apt update and apt upgrade, but MacOS users have to wait for Apple to update their computer.
The OEM phones are cheap because the manufacturer sells them at a loss, recouping money by locking them down and pre-installing certain software.
The alternative is that Google is properly regulated, or cheap smartphones phones don't exist.