When I asked a senior Apple executive why iMessage wasn’t being expanded to other platforms, he gave two answers. First, he said, Apple considers its own user base of 1 billion active devices to provide a large enough data set for any possible AI learning the company is working on. And, second, having a superior messaging platform that only worked on Apple devices would help sales of those devices — the company’s classic (and successful) rationale for years.
This is pretty much the expected and logical reason for not expanding iMessage to Android. With services such as Apple Music, the company makes money off subscribers. However, iMessage on Android would cost them potential customers.