Grammer and punctuation has traditionally been an indicator of education and background, this is also applied to memebers from non-english speaking societies, whos brightest demonstrate a robust command of not only their own language but English too. I believe alot stems from that.
In my experience the shaming is more from pronunciation, as words take either new meaning or sound different from what's expected, and its easier for majority speakers to shame based on that and feel as if theyre experts, and find a common point to feel superior.
It's not nice of course, gently making fun of a few words here and there is OK, Its usually met with a smile, but shaming is nasty and unpleasant, almost like bullying.