Because their intention just invest for short term investment. I hope you know before the coin end up with zero value the altcoin price will touch a high price before when it has launched on the exchange. So, that is the chance for investor to sell the altcoin and find again new altcoin. It is being a culture IMO, moreover for those project who use an IEO as their way to launch their project then there will be many investor who will get interest to the project.