Because altcoin world is too large comparing to single currency on top BITCOIN, how can you speculate a thousand currencies when bitcoin is just there always to show what is the movement in front of us.
Bitcoin is still a coin that cannot be beaten by many altcoins now because what is seen in the market is very accurate evidence that when Bitcoin starts to move up, the altcoins follow it and vice versa, so obviously altcoins will not be able to beat Bitcoin if the movement path is still like that