Why do SEO companies not practise what they preach?

Bit of free time today so I thought I would research SEO companies. Most of them state all the things they can do for you, but why don't they do it for their website? A classic is the html and xml site maps. It seems like a forgotten item for most webmasters, but it is very very important. Don't you forget.

More info at Website Sitemaps and examples.