Is not something out of the blue, it was planned… Apple actually try to cut it in half, 2 years ago, to make it smaller, but since they were changing the standard anyway, better get rid of it.
I see it as a both user and business oriented decision: the airpods connect to the iPhone very easily and so any other Bluetooth earphone, is not a hassle to connect anything to a phone nowadays (people already have Bluetooth speakers) and it’s a one time thing; you can add more things to the earplug now, it can be smart, measure vital signs and maybe improve hearing. Do you know the Research Kit? It has something to do with it too, once the tech is spread they can improve the AirPod and gather more data from more people, contributing to medical research.
Apple is one of the greatest smartphone companies, this changing is not only beneficial to them, is for Sony, Audio Technica, Seinheiser and so on… Every audio company will have to up their game about wireless headphones. Sorry but it’s a bit shallow to think it trough Apple’s the perspective only. Search for wireless earbuds on kickstarter to have a glance on how they are going.
Two more things, as far as I’ve read/watched, they don’t fall of the ear easily; it’s not like Apple is putting something on the way of customers when they want to listen to music… people will have the dongle and will have corded earpieces. It’s a first move... I think it’s way more serious to have a single port on the MacBooks, for examples, and nobody is talking about it anymore.