One issue they face here is that for most flights, the time wasters aren't what happens once you are in the seat of the plane. It's everything that happens before that at the airport.
Usually, I breeze through with TSA Pre but neither myself nor my car service likes to bank on that. (Also slowdowns on my >1 hour drive to the airport.) To your point, even if it's not security, there's a certain amount of overhead and buffer for a lot of people going to the airport for a flight.
