Project fails because:
1: team failed to follow the whitepaper
This is mostly, moreover if they cannot realize their own roadmap, like the development of the projects, listing on exchange schedules. Additionally, the lack of funds also becomes one big problem for a project to rise up and develop. If they cannot gain or collect enough funds, they will easily fall down. On the other hand, sometimes, a team also only focuses on how ways to gain money, much more money to collect, but after getting the money, they don't care enough about the projects and leave the investors and community in the confusion and no project development. This means that the team focus only on the money, not the project.
which of the old projects will you like to see coming back again to achieve its original project idea to solve some issues facing the cryptocurrency industry at the moment and why do you want to see them back identify the real-time problem that coin can solve.
If that is about the top coins, they still have the chances. But if this only the old coins but they have no development, I don't think they have a chance. They may be dead projects and cannot be lifted up again. No hope for worthless projects.