Not only the alt coins you mentioned have dropped. Currently we experiencing a full bear market and almost all alts are down.
They have certainly dropped considerably since I bought them and that was also when the value of BTC was much higher, overall I think they are worth about a third of what they were when they were at their highest (while I have held them).
Perhaps now we are close to the prices that are the cost of coins (the cost of mining for a given coin). And everything else is speculation.