Comment by numpad0

They all died. There were Linux phones until Android and there were some non-Android phones until Android 8 or so, such as Qt Extended, RIM BlackBerry OS, Palm webOS, Mozilla Firefox OS, and Microsoft Windows Phone, to name a few. They all died from numerous footgun wounds as well as pressures from competition.

VoLTE was one of major contributors to the situation, by the way. Only iOS and Android supported voice call on 4G LTE for first 3-5 years, due to it being a huge pile of TBDs and transitional hacks. There were political fights in whether the LTE is to be 4G or it was to be 3.9999G and superseded quickly by a completely separate 4G standard. This meant that companies and consortium that maintained alternative OS could spend unrealistic amount of lobbying and engineering effort trying to get into it, risking investments needed for it, or give up and start procurement process for a white flag. All chose the latter, and we ended up with an iOS/Android duopoly with unprecedented totality.