Just why are standards not standard?

The bug bear of every web developer and designer around the globe is getting a website to look the same in most if not all browsers. This task is made so much harder by the fact that every browser reads and translates the HTML and CSS components differently. Since the mainstream internet became available to the public, HTML seems to have just about be adopted as a standard therefore making simple, un-attractive and outdated websites just about usable (not counting the arguement of accessibility of course). CSS however has been adopted several different ways by browser manufacturers. Even some browser versions differ in the way they show CSS elements! Can it really be that hard to look at the W3C standards and implement what they state. This would do away with all the well known Box-model hacks and the like making way for useful information on the web like new special effects etc and a progression of ideas not just how to fix what we almost have already.