It’s a question I’ve asked myself a few times over the years. I am not the most literate person in the world but it does make me laugh to see some of the miss-spellings. Now, the most common places to see this are in non-native english speaking countries. Weirdly in Paris you get lots of graffiti written in english but obviously not by native speakers. I presume because they are “talking” to the english speaking viewer?
Anyway, here is an example from my own hometown of Glasgow…where it could be argued english is also not the native language, YA BAM!