Aside from the obvious reasons of competition, Beeper also used Apples infrastructure, that Beeper was then going to monetize. Not too surprising they shut it down.
Yes. I did mention APN (Apple Push Notifications) to Beeper Push Notifications which then routes via FCM for Android.
The whole setup does require active server cost + time to work on the app to bring it to parity with iMessage Features.
Apple could have seen it as an opportunity to monetize the partnership (and make some money from Android users) but deemed the exclusivity to be worth more than opening up in a controlled fashion.
Apple already knows that iMessage, alone, is a huge selling point for their iPhones. They held out for a few years keeping iTunes away from the rest of us before finally giving in, but I very much doubt that they're going to open up iMessage any time soon. It's pretty much the only thing that keeps iPhone users in their ecosystem anymore.
That's true, but it would be more Applelike to develop their own app. They obviously know how to do it, then they could have 100% of the profits and not have to deal with a partner. But Tim Cook said they re not interested in doing anything like that.