iMessage with macOS works fine on non-Apple hardware. Perhaps you intended to write iOS and the iOS version of iMessage only runs on Apple hardware? Or was it more a point of legality? Or end-user acceptance? Or availability to the general public?
I'm intentionally trying to point out that the generalised statement was wrong without context, while at the same time providing wording that would probably match the intended message instead of the one that ended up getting posted.