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.
If the dev team are not honest and just want to scam people,they will just use the coin to collect funds then run away,but if they are transparent they will continue developing more projects for that coin until the price increase.
There are many times that this happened those devs are just getting some investors just to make their development get a lot of investments. But in the end, when they are able to collect a lot for their ICO. It comes to an end already and they are becoming gone and their development ends there when they have their bitcoins investments already in their hands.