Why do you think good altcoins fail to keep going? It seems there are some that are good and people collectively have put in tens of thousands of hours supporting, but the team decides to give up midway.
In my assessment and observation some of the altcoins are not transparent to their investors they just hyped them then they will show good standing for a couple of weeks after that they run away, or sometimes the developer is scammer unknowingly, or lack of team work and group effort. That's what I've been thinking about it.