In the case of smartphones, they do have a choice, and a lot of people still choose iPhones and some even Samsung. Hardware isn’t really an area locked down like internet services are.
But the “stacks” in the play store. There is no google play.
There's no google play because China banned Google.
China banned Google because Google refused to remove censor politic contents.
That contents mostly from An anti-CCP cult called FaLunGong and some other dissidents which all supported by the US.