If you're asking why bitcoin is placed as the top currency, the reasons are pretty obvious: it's because it is the first cryptocurrency ever traded with real money and its price on the market. Most cryptotraders are banking on bitcoin due to these reasons, with (sadly) its technological implications and flexibility trailing behind the price. You can also factor in the amount of money invested in infrastructures surrounding bitcoin, mainly the mining scene. Due to this, people who are knee-deep on their involvement wouldn't want to get their leverage and advantage on investments be turned to nothing. I'm sure there are a lot more reasons why people choose bitcoin over any other cryptocurrency, but these, I think, are the most probable reasons why they stick with it through the highs and the lows.