This is a serious question and i know a lot has never knew why it happens like this. When ever Bitcoin is Bullish almost every altcoin will be Bullish and when Bitcoin set an all time high so as the rest, though there are others which are repellent to Bitcoin they just go on the opposite direction.
What Could be the reason for this?
Let me give you a real example and if you have some basic knowledge on Forex trading this will be easy to get.
If the US Dollar index is showing that the US is weaker then the US will be weak against all major currencies e.g EUR/USD or GBPUSD. Then there are cases when you will findout that the US Dollar index is weak and you expect the Euro and Pound to be bullish but maybe you will see only the Euro bullish and the Pound bearish or maybe bullish to some extent. So this means that the trend of these 2 are not fully determined by US Dollar index. If there is some news in the EUR Zone this will affect currencies like EUR, GBP, CHF and these will all fall against the USD and other major currencies. So it just happens coincidentally if the USD index moves the other way and the other major currencies the other.
In our case Crypto currencies are the base currencies and stable coins are the quote currencies e.g BTC/USDT or ETH/USDC. Investors always look for an asset which is profitable, so if they see the Bitcoin to be bullish they might sell off some other assets and invest heavily on Bitcoin, so it also happens coincidentally that When Bitcoin is bullish some assets will see and when it falls the rest might as-well fall and investors convert to stable currencies.
Volatile Altcoins & Stable Coins
Bitcoin is an ancient altcoin and is a volatile altcoin, so whenever it goes up it has to correct after sometime. The only difference on VOLATILE ALT-COINS/STABLE COINS and currency pairs like EUR/USD is when EURO is going up it means investors are selling Dollar so that they can Buy Euros. On the issue of Volatile Assets/Stable Coins the Volatile Assets gain or lose value but Stable Coins they don't change. They are just a store of value only. So investors will be selling volatile coins which means they will be taking their profits and buying Stable Coins to safe keep their portfolio value.
So its now like Bitcoin in the one which drags everything down but its the volatile altcoins which will be moving and the Bitcoin just happens to be the major player with much dominance.
If we would say Bitcoin drags everything down with it then it means crypto currencies are not decentralized, so Bitcoin moves when volatile altcoins are moving not the other way.
