I'm with the OP here.

I recently went thru a 7 hour ground delay, and then an overnight stay in a connecting city, as a result of what I believe was UAL operations making a conscious decision to deboard our entire flight in MIA just before the door closed, so they could remove a part from our aircraft to keep another flight which had been rerouted to MIA on it's way to the Dominican.

Someone in ops apparently "did the math" and it was cheaper to do so, than keep the Dominican bound plane delayed overnight in MIA with the resulting financial consequences I imagine. I can think of no other reason frankly.

I got the compensation "I wanted" for Mrs KDS777 and myself, but not until after some serious back and forth with UAL on the matter.