Some of the reasons why I think some developers fail is because:
1. Lack of funding both the starting aspect and the launching aspect (lack of money to continue)
2. Failure in out righting frauds
3. Failure to evolve especially when the coin initially start bomming
Apart from the factors you mentioned, the influence of market weather is also very important.
Because so many fail to survive in extreme market weather.
some of them have to deliberately announce to leave their project or they just disappear because the market is so tough right now.
Apart from that, the failure of a project also includes the duplication of a successful project from a similar name or concept, they are classified as uncreative projects.