Remember, this whole thing about crypto is largely decentralized, thus, there is no single authoritative body in control of the crypto market. Although there are few centralized platforms among crypto, the market is largely influenced by the efforts and influence of the users of crypto. How well sellers and buyers treat the coins on the market affect the performance of the market.
I think BTC whales greatly impact on the market direction, they have enough funds to pump or dump any altcoin. My another assumption is that many big traders use trading bots that work almost simultaneously and when the market is going up (or down) we can see changes in the price of the top 10-30 cryptocurrencies. These are just my own thoughts...