When BTC dumps, all other coins also dump, it is worst thing because even if bitcoin dumps, then it should not effect the other cryptocurrency price value in BTC. i,e when BTC dumps the price value of altcoins is also drops while it should increase because btc downs. When people will realize it that it is not in their benefit?
You can call that any theory you want but the fact remains that bitcoin is the only coin the market that can be trusted and the rest of the coin revolve around the value of bitcoin and if people start selling bitcoin the rest of the market will go down as well and that is what we are seeing for years as long as the alt coin market came into existence. Most of the people are not long term holders and they will trade according to the market sentiments and that is why you see big drops in all the market.