It's pure psychology. If you're reading a sentence and the word "the" is put twice, many people will just read over it and not notice it. Or if you are reading a sentence and you see the start of a word, you identify it as something and later find out that it was actually a different word. Our brains latch on to certain things and forget others.

Another important factor to look at is social media. It's so easy to spread a false spelling of "Looney Toons" to thousands of people in seconds. Heck, it's like the tabloids. Some people read them and they really believe that Barack Obama is pregnant. People just usually believe other people.