-Overselling is a big part of it. But my first job used host gator and any time we had to do mass uploads they would temporarily disable our account for taking up too many resources. We had streaming videos, which you can bet they raised an issue about, again for resource usage. As we filled up our "unlimited" space more and more you can bet that support got worse and that the frequency of account disablings increased.

Any time we had a major support issue it took days to get it resolved usually. The staff that I had to deal with personally weren't friendly at all, and really had little to no idea what they were talking about.

The main root of the issue is the overselling though. Because they really can't give you unlimited anything, so they find other ways to prevent you from having it when you go to take it.