KDE Connect works as well as airdrop between iOS and Desktop Linux and Android, and isn't a unintrospectable proprietary protocol. (Which is to say honestly it's spotty, but so is Airdrop. It's the underlying Bluetooth that's at fault with both.)
Even then, Apple could choose to let their protocol be reimplimentable by others but they've chosen very explicitly not to. They've locked it down with Apple signatures that can't be used by competitors. As you pointed out, it's a competitive advantage for them to lock others out, so they have. It's working, but it's gross. We can dream about better, but for now, no buying books on the Kindle/Amazon app on your iphone, or buying video off Google Play on your iphone, or Chromecasting AppleTV to your Chromecast (just buy an Apple TV like you're made of money).
Even then, Apple could choose to let their protocol be reimplimentable by others but they've chosen very explicitly not to. They've locked it down with Apple signatures that can't be used by competitors. As you pointed out, it's a competitive advantage for them to lock others out, so they have. It's working, but it's gross. We can dream about better, but for now, no buying books on the Kindle/Amazon app on your iphone, or buying video off Google Play on your iphone, or Chromecasting AppleTV to your Chromecast (just buy an Apple TV like you're made of money).