iTunes was offered free so people could buy music and load it on their iPods.
If Apple spends time and money developing software like FaceTime and iMessage for other platforms, that's time and money they can't spend on software for people who buy their products. Also, Apple would have to support FaceTime and iMessage on other platforms, which would also cost money.
If Apple wants to charge a monthly subscription fee for FaceTime and iMessage on Android, that would be a different issue. I just don't see people subscribing to that like they do Apple Music, Netflix etc...
You do realize iMessgae and FaceTime server and other fees will be subsidized by Apple hardware sales? iTunes is a piece of distributed software, and to sell music no less. There’s a much better chance of seeing iCloud on Android before FaceTime or iMessage.