Those kinds of apps took off in other places because SMS was expensive, but in the US there has been cheap and/or unlimited SMS for a couple of decades now. So people had no reason to use anything else. That means when iMessage came along and transparently covered up SMS it became the standard.
It is especially bad for teenagers where the iPhone has almost 90% market share. If you are a teen using Android with 9 friends, chances are literally all of them are on iMessage. Good luck trying to convince all 9 of them to install another app just for you. Apple’s indoctrination marketing is so powerful that kids are actually bullied for not having an iPhone.