There are two reasons, the first people have ideas on improvement of life or the relations, they want to realize them. The second reason that some people just very cunning also want to receive money having brought together them from investors of ico.
You say "But there are also coins that are unique and functional. The problem is, those legit coins are very hard to identify." I think we need to step up our research and not get involved with scammers by thoroughly comparing what projects offer.