The same thing happens in the stock market. When one big name stock suffers, other stocks in the same sector go with it. It happens for a number of reasons. Poor performance of one company implies that similar companies will suffer similar issues.

So if the fundamentals of cryptocurrencies are in question (which will happen often with such a young technology) investors are trained to sell first and ask questions layer. The same herd mentality that drove up prices so spectacularly over the last month or two can also take them down very quickly.

As a long term investor in crypto, I try to ignore the day to day fluctatuatuons and instead focus on whether or not I still believe in the fundamental story - which I do!