Agree it seems that way but one possibility is crew timeout. If they hold the plane and crew tines out then nobody goes.

looking at the flight status the inbound plane from TPA arrived gate at 8:05 but the DSM flight pushed at 7:53. Would have been at a bare minimum a 30 minute delay to reasonably accommodate all passengers and bags.

agree it’s annoying but UA does have algorithms for these things. Given that it was a weather delay from TPA hurts too.