Well, I would guess that most young people—if they're anything like my son—are still living at home, so you can imagine the barrier to mobility would be the cost of not only travelling and finding work, but of course finding a place to stay, so there are a lot of impediments.
I would think—and I think this has been proposed in the past—some sort of subsidies around mobility would probably be a good way to encourage a little bit more mobility.