A friend of mine is a Khmer Krom native. His mom speaks Khmer and Viet. I talked to his mom and she said she was raised being Khmer living down there, simply because it was who she was. She told me she was forced to speak Vietnamese or else she'd get repercussions from the Viet army. My friend, who was born in Vietnam, spoke only Vietnamese. This is all he knows and can relate to.
I'm saying, this is how history works. Eventually, culture will be gone with the Khmer Krom people. The victor writes the history books.