I think we all use slang to some extent to express ourselves. But some people may not know there is anything beyond that for them or they may think that particular slang carries its own intrinsic worth so they use it as a badge or to show they are somehow "with it" or in the know. When in fact it is not very expressive at all but only limits their abilities to be individuals rather than just being a part of a particular culture. Might have to do with lack of education (formal or informal) , nor reading, or spending all one's time within a certain cultural group rather than meeting people of other groups than one/s own.
I think using it online is different than using it in person. I would never say "yo" in person unless just being silly with someone else who thinks it is out of the norm. I don't know the rationale behind that but it's an empty code i live by. hahahahahahah so much for "deep thoughts" by Jack Handy this morning.
I can venture to say they don't don't if it is the only language they surround themselves with. From the internet and friends to even their parents, they don't understand how degrading it sounds. Hopefully, it is only a trend and they can see by their books and other elders it is not the way to present oneself.
Sunshine 