"Don't it make my brown eyes blue?"
"Your mama don't dance and your daddy don't rock & roll"
I think that's true of the second example but probably not of the first. The first is more about flow and craftsmanship. That second syllable messes everything up. Also, if you look at the lyrics, you see there's a pattern being maintained. "I don't" is shortened to "Don't" ("Don't know when I've been so blue".) at the beginning of earlier lines. This use of "Don't" matches that earlier use, even though it's not short for the same phrase.
Don't know when I've been so blue
Don't know what's come over you
You've found someone new and
Don't it make my brown eyes blue