It is simple, it is through Altcoin you can easily multiple your money, for BTC to do X2 from the present price is bid deal, but very easy to see Altcoin do 2X, 3X in a matter of weeks
This is probably the best reason why people invest in alt-coins.
Also, there's quite a lot of them and you can always invest into a new alt-coin for a very,very cheap price and hope that the price will jump for a lot. It's just a best for trading, since it's more likely for a price to jump from 0.50c to 3$ then from 500$ to 1300$ quickly and in a short time.