It's human nature to give up after you realize that even your best efforts aren't good enough to change something. Smith is probably the worst starting lineman in the NFL. He played only ONE YEAR at left tackle in college, and it was a small college at that. What do you think these other players are thinking, realizing that they're playing with someone who doesn't even BELONG ON THE FIELD?
Go watch a pickup basketball game where a bunch of adults are playing with one kid about 10 years old. Every adult on the team will play softer than they usually do because they know they have a weak link they can't compensate for no matter HOW hard they play.