GM’s aren’t necessarily wrong but I think the main reason they add at the deadline is not because it increases their already slim odds of winning a cup. I doubt it changes the betting math by more than 1/10 of a %. They make the move/moves for job security because:
They feel pressure to signal to the owner that they are making moves to win now and sell tickets
They feel pressure from their stars and vets who have no problem throwing their lesser teammates under the bus to win now
They feel pressure from the fans to DO SOMETHING CHEVY (insert every other fan base to their playoff GM too)
Give the people what they want to throw shade on the loss.
Add a few pieces to cover your ass at a minimum and maybe even win a round.
Never underestimate pier pressure effect, and job security when you are getting paid multi million dollar a year contracts.
Not being cynical at all because you do not want to be the GM who stood pat and his teams got bounced in the first round.