It's just because of huge number of stupid altcoins under ethereum. In reality, Bitcoin dominance still standing.
Just be real, it's just more money coming to those ERC20 Token and many other alt coins, the bitcoin is currently stagnant at the same stage, even though the price of bitcoin heavily affect the whole cryptocurrency market, but the market capitalisation of the whole cryptocurrency market always increase and the majority of incoming money are going to those ERC20 token and other alt coins.