The success of a project does not depend on the developer alone mate, if it does, then there will be a lot of successful projects cus I believe no developer wants to start a project and fail on purpose,
The success of a project is tied to many factors and these factors are all focused on one common goal, "the success of the project" if one part does its job well and the other party fails in its duties, there's a chance the project might still end up a failure, and to give you a hint of what I mean, the community is very essential to the success of any project just like the developers is.
This is a good addition to OPs post. I agree on developers having a major role in the success of the project. Marketing, project development, etc. but there are smaller factors to this, investors or their community plays a huge part as well, if they only see a project as a money-making tool, eventually they will leave it without a second thought once they have reached their goal, which is to earn. Any substantial growth to a projects market price will help the project to develop it further, so if investors leave and the price starts falling everything else follows.