Mostly because they have been caught in the old hodl paradigm that was good in bitcoin times but no longer. Now it is all about being on top of the market and the ICO opportunities to make cash.
HODLing is actually investing in a coin you have faith would appreciate sometime in the future and incidentally the prices of all coin went down in recent times, so it was an ample opportunity for people to stash their favorite altcoins and then wait for when the expected would come through and it does!
There is no sense in saying HODLing ended with Bitcoin and it's now history, because must Bitcoin enthusiasts saw an opportunity when price dropped below $7000, now check the price today and see what you missed. Same goes for the established altcoins.