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 can buy very cheap a very large amount, where with bitcoin you can not
altcoins less risk? i wouldn't say that when altcoins are constantly losing most of its value in less than a day. for people who like to gamble, altcoins are the place to be. for a normal investment with long term potential, bitcoin is the best possible investment. short term wise bitcoin might not be ideal, but long term nothing can beat bitcoin.