Because for most of cryptos existance you could only buy BTC from places like coinbase. They've slowly added more entry points and entry coins, but almost all trading is done between BTC and another coin. So naturally if the trade price in BTC for a coin doesn't change much but BTC moves, the dollar chart of that coin will look very similar to BTCs
Most cryptos rely on the price of bitcoin heavily. I'm sure someone has a good explanation as to why that is, but I do not.
Because for most of cryptos existance you could only buy BTC from places like coinbase. They've slowly added more entry points and entry coins, but almost all trading is done between BTC and another coin. So naturally if the trade price in BTC for a coin doesn't change much but BTC moves, the dollar chart of that coin will look very similar to BTCs