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.
Altcoins are similar to any other product so why an altcoin fails, lack of support, lack of development, not enough investment, sloppy management of resources human monetary, lack of marketing or a bad marketing campaign and that is just the beginning.