The reason for the decrease in price of other cryptocurrency coins with bitcoin is that almost all coins are listed on the exchange in bitcoin pair, so if the price of bitcoin decreases or increases, it automatically affects other altcoins. For example, if the price of a token is 100 satoshi, then if the price of bitcoin increases, it will definitely increase relative to the dollar, if the price of bitcoin decreases. The price of that token will fall against the dollar. this is how the price of the token in the market fluctuates with Bitcoin
This as well, plus considering that when you think of crypto, you know you're dealing with Bitcoin but then you found out that there are whole plenty of coins out there. That's what my thought process at the least back in those days of my first few days in crypto.
ETH is also worth mentioning in token pairs. I see that pair quite a lot, well because it is non-Bitcoin.
Hughes token or coin is in ETH pair but ETH is in Bitcoin Pair so when Bitcoin price goes up, ETH price goes up and that's why ETH pair listed coins also go up with Bitcoin price. You will notice that the price of tokens that are paired with stablecoins like USDT, BUSD, USDC do not have an instant effect on the rise and fall of Bitcoin price. this is how the market works