Comment by immibis

They are probably not monopolies in the legal sense, since there are three of them with comparable market share and they also compete with the PC, which is open. I suspect there would be more pressure to do something about it if those weren't the case.

Apple sells something like 70% of phones in the USA due to network effects that might not be apparent to users in other countries - social shaming for not using iMessage. The European equivalent is WhatsApp, which the EU is forcing to open up.