most of the coins now a days are scam the main reason behind it is market is down and new icos coins cant able to resist to downtrend of market and they are selling and leaving the market
I don't think so, if this scams are really existing and there are a lot of it, maybe when the price of bitcoin moon last year we have seen them down.
But no, it did not happen, altcoins were only down when bitcoin was dumping so that is all related to bitcoin and it dictate the market movement.