Over the years, I have noticed that every time Bitcoin's price goes down other alt coins follow suite. And When the price of bitcoin increases, it’s expected that altcoins go up in price shortly after. Presently as bitcoin price reduced other altcoin prices was affected too. Fact is that Bitcoin has the most secured network and it was the first among others. No doubt some alt coins was made of bitcoins clone.
But being that a product can be the first of its kind to be made (just like Bitcoin) and other companies may decide to produce similar product;( just like alts) but that doesn’t mean the original product price and value will always affect others. So why does Bitcoin have such a big influence on other alternative cryptocurrencies.
Bitcoin was the first and that is likely to keep it as the primary cryptocurrency for a long time to come. People use it's price as a gauge and it usually has at least a loose correlation with all others as you've seen. Many people will use the price of Bitcoin to figure out which way the market is moving and if it's going up they'll start pouring money into other cryptocoins as well, hoping to find the next unicorn to ride. You try to associate logic to the movements and might be able to come up with some rough ideas, but it gyrates much like the stock market - it's using massive pools of information along with the prevailing emotions of every buyer & seller at any particular moment.