More often than not, the reason is for quick/fast profits, Bitcoin is a long term project and as such quite a lot of investors do not have the patience to wait for the long period, so they go after altcoins (short term projects). I am pretty sure 9/10 of investors that invest in altcoins are well aware of the risk involved, but they still go ahead with it cause of the chances of a short pump were they could make ROI. The thing is this, even if anyone must invest in altcoins, make sure you have no intention of holding it for long, if you are lucky to buy at the right time when the coin is just about to pump, sell once you get your ROI and leave the project, most of them have no utility, so they are not sustainable for the long period.