I'm selfish when it comes to weekend mma. Someone missing weight (so much that the fight's off) means it's very hard to find a good replacement on a days notice. With USADA, most are busted with random tests way before or after an event, so you can still save the card.
If they can still fight you usually get a lesser version of them or a size mismatch, so continuously being over is the UFC's fault for not making them fight at a higher weight, and it's just irritating to watch.
But steroid use is a bigger offense.