Lots of factors. Most, if not all, old altcoins have dropped dramatically in worth.
Main one is no altcoin has taken off as bitcoin's silver. Litecoin was for a long time but it has languished too. Until people start using cryptocurrencies as currency the scene will remain a school boy's pasttime of playing/trading marbles. The boy's like shiny new marbles.
At the present time altcoins only reason for existance is to be traded for btc which really has value.
Hang on to your peercoins. The developer has not abandoned it and it has stood the test of time. Who knows what the future will bring.
I think you hit the nail on its head.