They might not want to solve it, but I don't think we should accept unethical business rationales.
I am somewhat resentful of Apple because as a currently-Android but formerly-iPhone user I am now unable to text some iPhone users in some situations because of iMessage. I guess fucking me with their bugs is a positive business outcome for Apple, especially because they create a environment where their bugs appear to be Android bugs. But that's an unethical stance on the part of Apple.
Now I just need to convince my spouse to switch
That's literally the opposite of what Apple wants.
Apple phones can send texts and communicate with any other phone on any other network and vice versa. They just don't use iMessage to do so. I can't DM my discord friends from my work Slack, for example.
As for why it's anti-trust, it's right there in the WSJ article. Apple executives are explicit in the lock-in being useful for their market power.
Also it may have been years ago but I'll never forget the way Apple originally captured phone numbers into iMessage. Once a phone number was registered in to iMessage no Apple system would ever send SMS to it again. That created a major problem if the owner of the number had stopped using Apple phones. They were sued over this lock-in and finally implemented a way to release your number from iMessage jail. It's still kind of awkward though.