Why do people use stupid spelling mistakes on purpose?

Basically everywhere on the internet there are stupid captions, phrases and words that look like they were written by someone who learnt English as their tenth language. Eg: mai, teh, wurk, heer, cyoot, moar, cheezburger, onleh, capshun etc and also using words such as "has" instead of "have" ie "I has cheezburger". Apparently they started off from genuine spelling mistakes, but a lot of them look too retarded to have been mistakes, so are they meant to look "cyoot" or something?