While that’s true about Microsoft with the Xbox (and even Sony with the Playstation — a company that originally wanted to partner with Nintendo), the smartphone business is very different.
Thanks to apps, content, and things like iMessage, there is decidedly more lock-in in mobile. Yes, the video game consoles have some lock-in with their games, but because the business changed so much generation to generation (with mixed backward compatibility results), there were obvious “switch points”. That’s not quite the same with mobile.
More importantly, Microsoft (and Sony) could get into the gaming business because they could buy their way in with the large publishers of games. So far, that hasn’t worked for Microsoft with smaller app developers. While money is money, time is often more valuable to these small teams. And they’re not going to waste time on a platform with relatively few users.