1) Availability
2) Ignorance
3) Committees
4) Comfort
5) Momentum
6) Passivity
Since reading "Good to Great" I see so clearly why most companies never get to great. Good is definitely the enemy of great and these are six good examples of that. Click through to the article to read a short definition.
I believe 3 and 4 are the key ones I have seen. The more people are successful, they tend to not want to push the envelope because they are "punished" if things don't work. Committees tend to make things harder to accomplish greatness, because there is always too much compromise. Small groups of people make greatness.