Could be for a lot of reasons. Not enough marketing, didn't reach their target, math didn't work out, so on. Or it could have just been a scam from the beginning. 
I definitely agree with your opinion mate. Marketing is one of the most important factor to consider when in terms of having huge number of audiences and it can reach to a lot of investors worldwide but what had happened is that they are now afraid to invest due to projects that were used as a frontline by those opportunitic people behind a specific project. Once they have reach their target they abandon and tell everyone that they have failed. I know that not all of them and some other projects trully failed due to lack of support.