Another reason airlines don't care as much about de-planing times are timed by the DOT if they left the gate on time, and did they arrive on time. There really isn't a metric for how fast does the plane empty...so other than the ULLC's that try to schedule a 20 minute turn there is little incentive to try to rush people off the planes.

Many people have said before, most people are already in a hurry to get off the plane, even if it's only to wait at their next gate or the baggage carousel.

And for those who are connecting, if the plane is delayed much, nearly everyone is going to be in a big hurry and there is little need to make a big speech about it beyond the typical announcement of please let those with connections off first.

Virtually nothing the airline can do to speed it up, it's not like the FA checking for an onward boarding pass for everyone would SPEED UP the process. Even looking at seat assignments would be imperfect at best as they could easily be different than the manifest when people trade.

I think even if bags were free, it would be of limited use. Maybe instead of 10 minutes it would take 9. Even w/o cost most people want to carry on whatever they can so they don't risk damage or loss of the bag.