Microsoft does not want IE to work according to standard and they don't want to provide a full featureset. A lot of smart people work at Microsoft, it's not like they can't figure this out. Microsoft's business strategy involves differentiating IE in basics like rendering and performance so that you have to buy Windows, test your websites in IE, and I think they still hope that they'll return to utter dominance one day. In so doing, they want you to decide that it's only worth your time to support IE since that's what most of your userbase uses anyway, thereby also requiring Windows for the web.
They won't support HTML5/Canvas fully until IE13 at this rate. It conflicts with their proprietary Silverlight technology, so any implementation of such in IE is going to be broken and incomplete, as we've come to expect as the standard.
Microsoft wants Windows to be mandatory for web surfing. That's the goal, that's why IE still exists.