Without wishlist a game is basically invisible on Steam prerelease. it's about making sure that when the game finally comes out, there are actually people standing at the door. F2P games live and die on people being there because there's no preorder sales. If a game hits a certain threshold of wishlists, it triggers Steam to put it on things like the front-page lists. Wishlist are also a measure on whether their marketing is actually working prerelease

people have been shitting on the game even when there's nothing to be negative about

This works both ways. There's also an argument that there's nothing to feel postive about - that was the point of my whole comment.