The tide seems to be changing, however: Apple said last month it would be opening up its Messages app (likely due to European regulation) to work with the newer, more feature-rich texting protocol called RCS. The company revealed as much in court documents, saying that putting iMessage on Android would only "serve to remove obstacle to iPhone families giving their kids Android phones."
Social pressure to convince friends and family to move to iPhone is by Apple's design. Apple's iMessage has become a mainstay in American communication and affects how people interact with one another.