There are many factors that can cause a project to fail:
1) The team behind the project is not that adequate team and does not have the experience needed to run an ICO or the altcoin itself.
2) The project did start as a fun thing and it was not planned that it would go so good (like TRON) and then they started to think that hey we should be serious now.
And many other factor that I can't think of them as there are a lot.