Why would anyone want to use Windows (Mac OS X) as their everyday desktop (or laptop) operating system?
Really, why? :)
Windows/Mac OS X do not have less problems, they just have different problems, lots of them. And 'they' (MS, Apple) make you pay time after time for a chance to get those problems solved, and new problems created. Why anybody on earth would want this?
The only reason - people are forced to used WIndows/Mac OS by hardware manufacturers vast majority of which doesn't offer OSless options. Imagine what would happen if Windows/Mac OS X would not be included into each PC/laptop price, but sold separately? Right, their market share would go down very-very quickly.
So, it's not an average consumer choice it use Windows/Mac, it's that an average consumer doesn't really have other options.