I think bitcoin affects some cryptocurrency because the main market uses bitcoin. So if bitcoin goes down and ups also some crypto currencies follows bitcoin. The impact is always there. So don't worry about it because it's been nature in the crypto world.
This is true to some cases though I do not expect each alts to just follow Bitcoin price movements literally. I can still recall when I was tempted to day trade Bitcoin before, but I was trying out altcoin. All turned out to be losses just because I went for the shitty coins.
Bitcoin was kinda it is bearish days that time so I kinda understand where my losses came from.
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.