Wow, what a problem to have. 7 billion page views per month but your site is aesthetically bland; subjectively “busy”; perceived, by some, as hard to use.
What about the page views? They account for something. I suspect people are getting things done on craigslist and getting things done easily. There are literally thousands of websites that cannot seem to offer even a basic value proposition and deliver on it with simple effective utility.
Usability still eludes major company business year after year. Microsoft continues to sell applications that are unreliable, hard to use, and filled with features the majority of their users will never use and people focus their energy on Craigslist aesthetics. That explains a lot about the current state of usability for the majority of websites and applications today.