Another data point at DFW on Eagle (Envoy) on a ERD today, 4:25 departure, leave lounge at 3:52, get to gate at 4:03 and they are paging “for an on time departure”. . . .
My 2018 experience is this happens frequently with Eagle flights at DFW. GA's have told me it is to have taxi-time cushion so ATC can't mess up their slots.
We have more than once been on time, but already been replaced by standby passengers. Got on but relegated to much worse seats than I had snagged. No I was not happy but I learned some things just are. Yes I have seen them close the door. I would really not be happy if they left me.
Of course in an earlier period of my life I was frequently the standby traveling for business on very short notice just hoping they would give me somebody's seat because I was supposed to be somewhere by morning.