I think, bitcoin has a big influence on the market, so if the price of bitcoin rises, there are many other crypto that prices rise too, because many crypto have prices based on the price of bitcoin
One thing is well known to all of us that Bitcoin is the base currency and we know that other crypto coins have same nature as of Bitcoin so this spread the same perception. When the Bitcoin price falls then people think the same about other crypto coins that is why it has affect on other crypto coins as well, when it increases in price other coins also start to increase in value.
Bitcoin's dominance is over 50% in market. It's mean all altcoins are based on Bitcoin. And, surely, the decreasing of the price of Bitcoin causes people to panic and all prices move down.