BTC is the first cryptocurrency creation and coin leader in the market such as the first seniority project, 1st trading volume, and 1st capitalization.
There are several reasons that altcoins price is up and down like BTC.
1. Traders pay attention to the market price of coin leader
2. Coin leader is a favorite investment with altcoins projects.
3. There is a very minimal altcoins project and got less influence from BTC caused some certain circumstances.