It is fairly common for carriers to do all that they can to keep passengers from "jumping ship" on what may be shortish delays because W&B needs to be recalculated and then checked when even one passenger or bag is offloaded. During busy periods, that can add 15-20 minutes to the departure process.
Part of this is complicated by UK rules requiring that bags be pulled when a passenger is offloaded. The US abandoned this rule 14 years ago when it subjected all checked bags to TSA screening. Carriers are free to set their own policies and generally do not pull bags when the separation of passenger and bag was not forseeable at the time the bag was checked.