Go on any blog site. Heck, even browse through the questions on here. You quickly realise just how stupid people can be, and how badly they mangle English. Now imagine what that would be like if nobody took an English class.
Also, English is the single hardest language to learn in the world. Right now, I can guarantee there are things about the English language that you do not know, just because there are so many different rules and exceptions
The students have to take the English classes to enable them know the proper use of English. The spoken English is different from the spoken and most do not know the verb,noun or the proper use of English elements.