because of what they are not ...
Without having to become a pro-Microsoft advocate, I think that most people would agree that Linux's main appeal comes from the fact that it developed on the fringe without any commercial help. It attracts users/ developers who are willing to get it to work.
Linux's future success and survival will depend on its widespread adoption by end-users.
It's important to note, that for them to adopt Linux, the novelty of something non-microsoft that requires larval time to set up and get working just won't be enough.