The people doing an ICO do it to raise a bunch of money, much like a kick starter campaign. The people buying an ICO buy it for a quick buck and a lot of times they end up selling these coins from the ICO for 10x, see BATs.
The allure for people starting a company is that you can raise millions and give 0% of your company away. Some people will scam, it's true maybe a lot will, but some will undoubtedly start something big and will want to do more than just scam.