It is for the US Army. They are the initial customer anyway. Civilians are the best beta testers. The internet was originally created to have a network in place for the military and I see this as the natural evolution beyond hard wired systems or intermittent wireless towers.
I think it was dreamed up as a way to monetise the increasing capacity of SapceX launches. They might run out of customers and so they need ways to make money out of launching. A constellation of 10k+ satellites is a good way to need lots of launches!