There are several theories, but most experts agree that altcoins (coins alternative to/other than Bitcoin) rise faster than Bitcoin in a bull market (the period when prices are in an upward trend) due to the demand of investors switching to these altcoins in search of even higher returns than what is available from BTC. Many of these altcoins are still in their early phase and often growth can be stellar. Moreover, the EC10 is subject to survivorship bias. This means the strongest coins with sustained price momentum remain in the bundle, while those weaker coins with price depreciation will fall out of the bundle. When these weaker coins fall out of the EC10 bundle, they will be replaced by stronger coins which the market favours.