To say the truth it's not easy to be a developer, not all projects that failed are bad, they might not just meet their expectations
They failed because they don't have enough funds to spread awareness to thier project. That's why many bounty hunters don't link to promote them because of low payments. And also creating project now are risky because many bounty hunters and investors victim of scam campaign before. That's why if you are developer you need to have huge fund to promote your project and also you need to be transparent because this is the number 1 needs to gain more trust.
For me project failed because their funds are not enough for the demands of the joiners, that is one of the reason why project become bad in the eyes of people. So we should very careful of choosing a project because there's a time can encounter a project that only used us but don't get any from them. It better to find project that gives you transparency about their created project.