They all fell down on the lack of apps.
If your phone doesn't have apps for Facebook, Instagram, Twitter, TikTok, WhatsApp, LINE, tens of thousands of banks across the globe, credit cards, transit cards, various government ID schemes (try booking your vaccine in Sweden without an iPhone/Android) etc etc you'll never make it.
You have to start somewhere. If there were a good alternative, then adoption of it would drive gradual availability of these apps.
Look at the desktop - we have Windows and Mac (and for a while it looked like we'd lose the Mac), Linux is still a desktop also-ran.
Look at the web - it took Microsoft completely neglecting IE for 5 years before there was any momentum at all towards other browsers. And now we're back to web developers mostly neglecting Firefox and praying for the day they can drop Safari support so we're 100% Chrome.
Linux never became mainstream because of how poor the user experience was, not necessarily because there’s only room for 2 at the top. Even technically experienced people don’t want to muck around with drivers and deep-dive into configuration. Since few used linux, few apps were written for it.
I think there is usually room for new players, whether they have to usurp an existing one or have compatibility with others to do it.