You are absolutely correct. I’m an iOS user and have absolutely no qualms using anyone’s preferred message app (as long as it’s not WhatsApp, fuck fb).
People have always hated on apples Windows apps, the same is probably true if they have to start making android apps too.
It’s literally the correct decision for them not to make an iMessage for android, the only people demanding it are the people who aren’t buying their products!
You’re asking them to do work and open up their chat platform to other devices that are outside of their ecosystem and they have no os level control over. The security aspect of this in itself makes this not something “incredibly basic and easy”.
On top of that, there’s literally no benefit for them to do it. There are plenty of third party options for chat out there, and again, clamoring for them to do this work and maintain a product while still maintaining security for no return is entitled and unrealistic.
People making this argument show themselves to be naive to how software development and business in general works.