They probably did.
But others in the military, and pilots, will go through intense training for such events. It's not easy, the dis-orientation, and inability to unstrap, swim down, then up, not as easy as it sounds or appears. So folks panic, suck in water and struggle instead of remaining calm and taking their time to get the belt off and get the F out of dodge. Even if it's just a hit the button for release, the panic and struggling make it too difficult for some and they screw themselves.