The price and, ultimately, the charts on any given exchange are determined by the price of the most recent transaction. How can the prices of 100s of cryptos all move in the same direction at the same time?
They adhere to a general trend, with Bitcoin remaining the one that they largely follow because it is still the best cryptocurrency to use. Additionally, the general mood of one sector of the market typically affects the other sectors, thus when Bitcoin is down, it certainly raises a negative mood (for the most part) in the altcoin sector. Not to suggest that altcoins don't have their own market; pumps and dumps still differ from coin to coin, but most of the time whales are controlling how much a market pumps or dumps.