Well, it sometimes may be justified by simple typos, dyslexia or something of that kind. Or rather, I want to believe that this is the actual case, not just lack of basic grammar knowledge.
As long as kids are concerned, there still is a chance to improve the situation, as they are in the midst of their education, so this spelling acquisition may be built during the years of their studies. When it comes to "illiterate" adults, it is all about their own desire to better themselves and their skills of spelling. If there is no such desire, well, they might try something like Researchpaperonline.net to edit their posts, or even write them from scratch - simply not to appear unlettered in front of hundreds and thousands readers of the Internet...