Oh boo hoo they enumerated an enormous number of corner cases, handled backwards compatibility, crappy cables, all sorts of things. It also reflects decades of back compatibility and painfully learned mistakes (consider mini-A) not to mention some weird pathologies (weird naming like hi-speed/ full-speed/ super-speed).
It sucks that the standard is so complex that a small number of design houses and consulting shops will end up with a de facto cartel of understanding the Sacred Knowledge, but nobody's stopping you coming up to speed by reading the whole spec and doing a lot of implementing. But it's not like you can build a solid TCP stack these days either simply by reading the original late 70s RFCs.
And you don't have to use this spec -- you can still use RS-449 if you think the USB spec has become overly complex. In fact I used that in a design only a few years ago!