It's not a long-term problem because they're going to have to add support for RCS at some point, meaning Android users will have a similar experience to iMessage with their iOS friends.

Apple wasn't going to port iMessage to Android because there isn't any benefit. I can't charge people to use a messaging app, they're free.

I love iMessage, it's one of the reasons I stay on the Apple platform, but in a world where almost all my friends use some other app anyway, it doesn't really matter. Like I still have to have Facebook Messenger, WhatsApp, Snapchat and Signal installed in order to talk to everyone. iMessage is mostly great for less technical family members because they "get it out of the box".