I think there is a big advantage for bitcoin and other crytocurrency trading because the fees are a percentage of the trades. Also, the fees are very low, so you can make very small trades and the fees are almost insignificant.
lol, pure bullshit that the user is saying to upp his post count.
On topic, that's like saying why doesn't everyone just trade equities, or JUST trade commodities. There are different markets to bet on and they all have different risks associated with them.
Bitcoin has higher volatility (usually) that allows traders to profit/lose a huge amount in a short amount of time. Same could be said with forex though.