There were many choices in the past 5 years and all got wiped out because people want services (apps) not operating systems. Windows phones didn't sell because didn't have apps. Same for Blackberry, all Symbian phones, Samsung's own OS (don't even remember the name and lazy to google), cheap Android phones and tablets without Google Play. Most people can barely use Google Play, they couldn't side load apks. Don't come with Fortnite because that's for a specialized market.
There are many alternative browsers, search engines, email apps etc but mostly for specialized markets (geeks). Why would Average Joe install something else than Chrome or maybe Firefox even if it's not preinstalled? Just look at Windows, even with Edge and IE preinstalled Chrome became market leader because that's what people wanted. They had many choices but they chose Chrome. Same with phones, it wasn't Samsung, Nokia or Microsoft who forced people to buy Android instead of Symbian, Windows Phone or Samsung whatever.
Same happens with smart watches, non-Android ones exist but struggle and will be extint unless Huawei is right and people don't want apps on their phones. Time will tell.