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.
From my 4 years experience in crypto world I always seen bitcoin always do something what we don't expect even we are not ready to face this.
When it pump nobody think it could be so high. Again when dump nobody ready to see it could be so low in short period. Again people start to forget btc can do something unexpected for a while, then btc do that.
This will happen always in crypto market. But we have to trade carefully and don't be panic basically when people trade with btc/usd pair. Because today or tomorrow btc will make a new high. But in some alts (shit coins) is very risky.