If I earmark a particular portion of money for cryptocurrency, which of course is what I can afford to loose, I can still invest everything in bitcoin and wait for a long term profit.
If my intention is to invest in altcoins, then I will have to diversify.
It always be our choice, not just to rely on a single coin or two but to spread our funds into different coins will be good. But I invested in Bitcoin more than of altcoins cause we know how its profitable rate and surely we can make money in this coin. We experience drops by now but still, I have confidence that it will recover easily as we saw huge resistance in the market.