A lot of them are combination money-laundering schemes and scams. Someone who stole a bunch of shitcoins wants to "clean them up", so they create an ICO and buy

A lot of them are combination money-laundering schemes and scams. Someone who stole a bunch of shitcoins wants to "clean them up", so they create an ICO and buy their ICO-coins with stolen shitcoins. By doing this, they also inflate the "market" value of their ICO, which leads to increased popularity and others notice and throw some money in. It's not clear to me what proportion of ICOs are money-laundering vs. real purchases, but I suspect it is quite high.