It makes people hot, bothered and sexually excited to see people (or artistic representations of people) in tight fitting clothes, there is really nothing complicated to it. Yeah we can all be armchair psychologists or try and find the social implications that led to these types of creations but really that would be overthinking what should be a fairy simplistic form of entertainment. I dont understand a lot of fetishes and the more I think of some of the stranger ones the more I just see it as chaos. When youve seen all the things Ive seen, there comes a point in which you have to surrender that you simply wont be able to relate to or understand it all.
TL'DR everything is a fetish, there is almost no logic to it.