When bitcoin drops to $30000, this is a disaster for most traders who buy bitcoin and altcoins at a price high. We didn't expect bitcoin to fall this low, so causing altcoins prices to be dumped very deeply. For traders who have already lost over 25% in trading, then it is best not to cut losses because it will make lose some capital. So believe me, the bitcoin price will back up again and altcoins price will rise again.
If you are not doing leverage trading there is no reason to cutloss unless you know where is the bottom and buy at that price so you will have more quantity of that altcoin or bitcoin. Market will always recover from its crash, it is up to us if we have strong hands to hodl and not let our emotion affect by the fuds causing us to panic sell our holdings. Market crash only happens when many many fuds keep spreading together with some whales selling their holdings for profit.