Great answer by Benedict Evans on Quora.

In fact, it was not until Apple came along and broke the log-jam that a similar integrated model became possible elsewhere. Apple offered (generally the weaker) operators an exclusive hot device in exchange for what looked like a one-off relaxation of their usual approaches, and generally got it. Having broken down the door - flat rate data, no customisation, manufacturer app store, there was no going back and the other operators had to follow.