Why is the Facebook navigation scheme so terrible?

Considering what Mark Zuckerberg’s brain child has been valued at, and how many programmers they must have on their staff, why is the interface so crappy? It’s nearly impossible to find out what groups you belong to or what pages you’re a fan of. The various links and options are contradictory or overlap each other. The look of the site is bland and uninteresting. What it does is very cool for some folks. But why do the site owners let it continue with such a stilted, poorly-implemented scheme? I’ve seen many first-time websites made by web newbies that were far better.