StreamOfTheSky
Adventurer
I'm the referee. I volunteered for the job so that my friends could play a game. I'm not in the game. It's not my place to be partial, to use my power to rig an outcome. I will get my own turn to play, and someone else to referee.
DM is not just referee. He also chooses the opposition and the location, among other things. If you screwed up and seeded the PCs against a top 5 team it turns out they never really had a chance to beat, that's your fault. If "homefield advantage" works out for team Monsters better than you anticipated, that's your fault.
And even extending it to incredibly bad dice rolling... If one pro basketball team was nailing every 3 pointer it tried while the other team went 5 minutes with a scoring ratio of 2 scores : 18 attempts, as a referee, at what point of ridiculousness would you forfeit (not sure the proper term) the game because clearly something was rigged?