I dunno. I have a pair of black converse and 2 pairs of ballerinas that I use regularly, so I'm not really a huge fan of shoes in that sense. I guess it's because there are so many different kinds to choose from, and some shoes only fit one type of outfit etc, which sparks the need for more shoes that fit other outfits. It's really not some kind of huge secret. And I doubt that most women care about what kind of shoes men wear, as long as they aren't stinky and dirty.
It's kind of like asking why guys like sandwiches so much.
Why are guys so obsessed over watches and video games?
I'm not obsessed with shoes, but at least it does change your overall appearance. If you wear ugly shoes, regardless of how nice your entire outfit looks, the shoes can make you look awful. As oppose to a watch? if you wear one or not, you still look the same.
I walk barefoot everywhere. That's a perk living by the beach. I don't like shoes very much, I feel like they are annoying, I only wear them because I'm like scared of picking up something or when its winter/fall here, when I just through on boots and leg warmers and socks layered on.
Girls are obsessed with a range of different things not just shoes, also there are plenty of men who are just as obsessed with shoes. Besides what's not to like? Everyone needs shoes and if a woman cares about shoes she is going to care about her appearance too.