I believe developers saw the the vision of Bitcoin and try to explore from the vision  by introducing and making their own coin but they lost focus because they only have one goal in mind which is making money, forgetting the most vital ingredients in developing an asset. They forget that they are certain steps and strategies to undergo before accomplishing a good assets or goal.

Some of the reasons why I think some developers fail is because:

1. Lack of funding both the starting aspect and the launching aspect (lack of money to continue)
2. Failure in out righting frauds
3. Failure to evolve especially when the coin initially start bomming

Most developers have only one vision which is making money that is why many coins doesn't grow and they failed because they didn't see the vision ahead.