I have been in the cryptocurrency market for almost two months, I observed that when the market fell, the percentage of BTC always increased. The current percentage of BTC has accounted for more than half of the market. What does this mean? Can anyone give me an explanation, and why is BTC? not another Coin? Because in my opinion, BTC is affected by market volatility more than the Altcoin!
when share market down, crypto price goes up
OP, can you put that in a chart? I highly doubt that it's true!

Plus one.

But even if that is true, the chart would only be very limited, and therefore inconclusive, because you've been in cryptocurrency for just a couple of months. That means whatever pattern formed within that short period of time does not speak of the bigger picture.
BTC accounting more than half of the market means it has a bigger market cap than all the altcoins, which could also mean that it has more value than the rest of the cryptocurrencies. It has higher demand compared to all altcoins combined. It also means Bitcoin is more trusted or it has more supporters and investors compared to altcoins. As to the why, I guess that would be your part to dig up.