Student or Learner
Imagine that your sister has just come home, crying. You tell her to tallk about what has happened but she refuses. What would you say?
Why don't uou talk?
Why won't you talk?
**Neither a teacher nor a native speaker.**
Why aren't you talking?
However, if I only had the chance between these two sentences, I would clearly go for #1.
I would choose sentence #2 for such a case:
P1: When my father comes, I won't say anything.
P2: Why won't you talk to him?
If you refuse to do something, then you are effectively saying that you will not do it.
Imagine a small child, who does not want to tidy up their toys.
Parent: Clear up your toys!
Child: No. I won't!
The child wouldn't say "No. I don't".
And a common use of 'why don't you...?' is to make a suggestion: 'If that's the way you feel, why don't you talk about it?'