~Not a teacher~
They're using "don't" in songs because it makes the lyrics sound better and smoother. I guess because it only has 1 syllable. It's better than saying She doesn't, especially when a song is after a fast beat or something. And it's informal english. People use it all the time.
Another example - It don't matter.
Try singing Akon's song with "doesn't". "Nobody wanna see us together, but it doesn't matter. No.." It doesn't sound good, aye?
Student or Learner