I have a very non-scientific queue theory. It's called the "government worker queue theory". It goes something like this:
"Government workers will keep the backlog at a steady state size in order to ensure their job security."
My interaction with government agencies includes filing immigration petitiions (I was the sponsor) with INS (before it was USCIS or Homeland Security), getting passports renewed, getting a driver license and its renewals, etc. The backlog is always defined up front, for example, "it will take 9 months to process your immigration petition for person X". Since the actual time to process the petition is probably 4 hours, they sit on a 9 month backlog, always processing the ones that are 9 months old, taking 4 hours each. I've often wondered, why don't they hire some temps or do overtime and "catch up" so that it only takes mailing time + 4 hours? Job security!!! With the 9 month backlog, they won't ever get fired. The longer the backlog, the more secure they are. If the numbers of processors was doubled, they would work slower until the backlog was at the highest tolerated level.

I think the same applies to the TSA people. They are not business people in a free enterprise world. They are government workers. They are not paid X dollars for each person they process correctly. They are paid X dollars an hour, no matter how efficient or inefficient they are.