because altcoin are less risk, and the return some time is greater than bitcoin, if you buy very cheap, actually this is the reason, you cna buy very cheap a very large amount, where with bitcoin you can not
if trading alts i recommend the minimum to put in is 0.5 btc if you want to make decent profits
playing with position sizes of 0.02btc or 0.1btc will not make you good profits.
With btc you can trade with a small position of 0.02btc and just use max leverage if you wanted for example just to
Maximize profits.
Btc doesn't have to double in value for you to double your profits like in alts.
i think that there are exchange that permit leverage with altcoin, which would be even better, because you have also a great amount of coins, and the swings are bigger