Helicopters can to.
Speculating but what probably happened is they were flying VFR (visual flight rules). Simplistically this means they were responsible for avoiding the ground and other aircraft on their own and not dependent on an Air Traffic Controller. This is easier and more expedient.
Along the way it sounds like the weather got worse than they expected. When that happens you can’t start flying IFR (instrument flight rules) immediately. You have to talk to the air traffic controller to get an IFR clearance.
If you encounter bad weather along your route you would try to orbit in VFR conditions until you received your IFR clearance. If you have mountainous terrain and crowded airspace like LA that makes a bad situation even worse.