The other factor is the that on U2 and others, they ask the passengers multiple times to clear their own area by waving big refuse bags up and down the aisle. However if you think Highlife can look a bit dog eared, you should see what they are like on Easyjet. At European locations BA would also need to move CE partitions, curtains and seats potentially, hopefully less so on Domestics.

I've seen NCL turn around a 320 in 25 minutes, admittedly they will have all the support crew lined up and ready to pounce as soon as the aircraft is rolling towards Gate 3. Still, given that some passengers do seem to take their time to leave the aircraft (at NCL they sometimes send someone from the back of the aircraft to shoo them off) it is quite an achievement to do it so fast.