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?
The simple term is pairs.
Just like what we see in the foreign exchanges, many of them have the USD in the majority and the same goes for most countries' economies. If USD moves higher this time, you see that other countries' exchange rate for their USD is also increasing but their local currency is getting weaker.
The same goes for the crypto, the bitcoin, and the altcoin market. Most of the time it is correlated but there are times that it is indirectly related. The majority of the exchanges have the pair for bitcoin and Ethereum and that's why they're moving altogether.