Bitcoin is not the one which determines the market, people are the ones who are affecting the market. The thing is, the demand for bitcoin is high and most crypto users are investing on bitcoin. No body wants to miss the rocket of bitcoin.
But you are missing the reason of why this is the case, people prefer to invest in bitcoin not because they are blind to the other cryptocurrencies, they are doing it because they understand very clearly that bitcoin is the coin that has the highest chances of being adopted all over the world and if that happens the profits that you are going to get with it are going to be impressive.