There is a reason on why alternate coins are called "altcoins" because they simply derive their existence on the foundation that BTC built.
Lots of altcoins are present in the market- whether memecoins or usable coins. The latter are the types where they simply took the technology of BTC but they introduced improvements therein. The former are the ones that derive their value based on influence and hype- where its value is totally dependent on supply and demand (ie dogecoin influenced by Elon Musk).
One of the many reasons on why the price of BTC influence these altcoins is because they derive their value somehow on how BTC is performing in the market. That is also the reason on why BTC has the highest price of all altcoins present in the market.
Though there are thousands of alt coins in crypto market only few top 10 or 20 are capable of being declared as alt coins that are worthy for investment rest are just shit coins (that's my own opinion). Crypto market is dependent on bitcoin for price and there is only one major reason for that i.e. BTC is the founding father of this market and there is no other alt coin till date which can match BTC security and decentralization nature.