Because AirDrop is already available on millions of Apple devices. If you start a new protocol it will only be available for a small user base and you need to ask Apple, Google and Microsoft to implement it.
That said, this is all just a bit of fun so monetising it isn’t really on the cards anyway :)
Saying that a platform shouldn't lock you in to specific proprietary approaches has a real & substantial non-personal advantage to it that mere personal preference doesn't encompass, as it seeks technical ecosystems capable of organic growth. I don't find your comparison quite valid.
Really you'll be happier if you just ignore everything going on with iOS and Android.