"Proper" English used to have a much more complicated grammar. When the Normans conquered England in 1066, French became the language of the educated upper class and English became the "peasant language." The once-noble English language was horribly simplified by all the illiterate peasants, who butchered the language by getting rid of all sorts of verb tenses, changing grammatical rules, etc. in exactly the same way that African Americans are doing when they hurt gendanken by saying "He be lyin', ain't it?" Eventually French stopped being trendy, but by then "proper" Middle English was gone forever, and only our modern, slangy, grammatically-corrupt version remained.