Double doors?

Why do businesses (mostly restaurants) insist on keeping one of their doors permanently locked?  If there are double doors leading into a restaurant, chances are that the left-hand door is locked.  Why?  Is it really that difficult to release the latches on the second door after unlocking the first?  Are restaurant managers afraid that too many people will come in at once?  Or do they see it as a source of amusement (“Watch this.  He’ll try to go out the locked door”)?  It’s not like people leaving the restaurant like having to wait inside behind a locked door while people file in.  Worse, this looks like a safety hazard.  In a fire, people will run towards the doors and the first person to arrive at the locked door will be crushed by the rest of the crowd trying to get out.

I think I’ll start pointing this out to the owners and managers whenever I find a restaurant with one of those locked doors.  Either that or I’ll just start unlocking the door whenever I can.