Ok, I finally have a solution.
Apple says this is a service, and they provide it to their paying customers (people who own Apple devices) free of charge. Makes sense, they have server, maintenance, security, and feature development costs. Can’t give it away.
Apple likes money and wants to grow their services unit. People like blue bubbles. If you want to use this on a non-Apple device, charge $15/mo for a login and make an app for Android, Chrome OS and Windows. Enough people will pay for it that it will make Apple a killing, because people are crazy and enough people would actually pay that much just to fit in. Maybe even more? Sad but true. Look no further than clothing brands. I don’t think they would lose a significant amount of users to Android because it still makes using Android and iMessages more expensive, and most Apple users genuinely like their products.
Problem solved?