I had a 40 point lead in the 4Q in my cup game, and my backups weren't being used. I can reverse my starting PF and PG and they will end up with 42-6 splits.
backups are the guys on backup spot ;) The engine is dumb, but you could calculate with it(if you don't blow out the enemy throug an accident) ...
Did you mean your last game, there every starter gets 18 minutes in half one, and a fast blowout with this lead is normal, but you are right that it is curious to play just the backups in this situation and not those guys who become less minutes in the game.