Two words: Bad Code
People sour on machines when there isn't a great code update until two years after the game is released. Transformers is a good game now, but it shot straight downhill. X-Men is a phenomenal game now, but the same issue.
On the flip side, AC/DC was great when it was released and has only gotten better. Tron, same thing.
I'm going to be a little controversial here and say that Star Trek doesn't have great code to make it a keeper. Now that the hype has worn off, owners are dumping it because it's a chore to get to a place where the game gets interesting (2nd/3rd missions, multiball, etc)