I hate when people use the phrase, "My Bad" in response to a mistake. Did we not all go to school to learn to speak, write and spell properly? I do not care if people do not speak eloquently, but at least use proper English.
But with this you expect everyone to be willing and interested in speaking proper English. The controversial term "ebonics" comes to mind as well as plenty of other forms of slang, not to mention region specific words (or even regional preferred words; Coke vs. Soda vs. Pop). To certain groups certain only certain forms of language are being perceived as "proper" English. And one can even argue how there's British English vs. American English and people might debate how proper English is the British variant.
Plenty of factors why someone doesn't use what you describe as proper English. Some might be nurture and external influence, some might be choice. And choice is a tough one; it's not like they can deport me from the country I'm born in for speaking a terrible derivative of my native language.
Though the best way to quit using "My bad" is to never apologize at all
