I switched to iOS (via a used iPhone on a BYOD plan) primarily for iMessage. I was tired of being the odd man out, missing out on things that were being planned via group messages, etc. Nobody was going to switch to an entirely different mode of communication just for my sake, so the existence of theoretical alternatives doesn't really matter. (And I do try to use Facebook Messenger for group chats, so as not to lock Android people out myself, since I've been on the other side of that and it sucks.)

But really this is Google's problem, not Apple's.

Google could have owned this space if they hadn't taken their eye off the ball and fucked up Hangouts. There was a period of time where everyone used Hangouts, and they did a brilliant job getting market penetration by including it in Gmail. It's cross-platform, so it could have been the lowest-common-denominator in over the top messaging services, the thing that everyone knew everyone else could use when you want something that's not SMS or kludgy MMS.

But Google snatched defeat from the jaws of victory, seemingly intentionally driving people off of Hangouts into other apps. This was incredibly stupid -- when you tell your users to switch to a different app, they may well switch to a competitor's. If they wanted to roll out additional features, they should have done it in Hangouts, not by building new services. (And RCS is garbage. I don't know who wants a carrier-dependent, unencrypted messaging service in 2019, but certainly not me.)

The lack of a viable iMessage alternative is entirely because of Google's failure to invest in the Android platform and produce one.