Why would Apple want to sell a lapdock when they could instead sell you the same thing + a redundant SOC (aka, a MacBook) and then high-margin cloud services to sync all of your data between your two differently-shaped computers?

Because most people with iPhones are buying Windows computers, but give them a cheap entry lapdock into the Mac ecosystem and maybe their next more powerful system will be a Mac.

Mac is a niche right now, iPhone with OSX could level the playing field.