What is the difference between,
Why don't you decorate the house yourself?
Why won't you decorate the house yourself?
Are both of these sentences grammatically correct?
And what changes when we are not making a suggestion to somebody directly but speak about something in 3rd person, i.e.,
What doesn't/won't Cameroon intervene?
What doesn't/won't she marry?
Why don't/won't these people leave?
Best Answer
Actually these examples illustrate a subtle but important distinction between what you want to do, and what you actually do. The use of will not/won't emphasizes the personal choice behind the action, rather than the action itself. Example:
Sometimes this distinction is trivial, but not always. For example:
Here Alan is asking Brian to clarify whether he simply doesn't make the effort to watch the news, or he actively chooses not to watch the news.
It's similar when talking about a third person, again emphasizing the distinction between what they do and what they choose to do.
Keep in mind that the "why don't ..." structure can be also used as a polite suggestion, so you have to be careful to understand the meaning from context. Examples:
"Why won't you ..." is not really a suggestion. It's more of an assertion as it presumes you have made the decision not to do that thing.