Apple did what they do, but their stuff is locked to their phones.
Google made their OS free for everyone. So now a phone maker can spend a HUGE amount of money building an OS and getting apps, or they can just use Android. Spending the money to not use Android looks like a folly.
Except Google trained everyone Android comes with the Play Store.
So either a phone maker has to contribute to Google’s stranglehold on the non-Apple smartphone market, making themselves a commodity, or skip including Google services and consumers won’t accept it.
So we’re now at a place where even if an alternate OS could get applications somehow, I can’t imagine any company being willing to put the money into developing it. Only a state like China could in an attempt to force Android out of their market.