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.
What altcoins do you have on mind exactly? What project was so good and got cancelled prematurely? Do you honestly think that if coin is good it will be shut down just like that?
There is always a reason behind it - either developer is untrustworthy (PayCoin) goals of the coin was set a bit to high (SpaceBit) or code of the coin is terrible (The DAO).