Information questions and suggestions often have the same form, but they serve different functions. Suggestions that are formed as questions can be analyzed as indirect speech acts. This is not the case with information questions.
Consider the question "Why don't you eat meat?" One interpretation is that the hearer is a vegetarian, and the speaker wants to know the reason for this dietary choice. However, another interpretation is that of a suggestion, an indirect speech act. The speaker may be advising the hearer to eat meat. Here's a possible context. "You know, it's important to get more protein in your diet. Why don't you eat meat?" In this particular context, it's clear that the speaker isn't asking an information question but rather making a suggestion.
The question "Why don't you eat meat?" is ambiguous. It can be either an information question or a suggestion. Both interpretations are possible. If we change the question to "Why not eat meat?" only one interpretation is possible. Here we have a suggestion. This can't be interpreted as an information question.
Though information questions and suggestions often look the same, they serve different purposes. Suggestions are indirect speech acts and not genuine questions of information. If we change the auxiliary from don't or doesn't to not, there's no ambiguity. Then we must interpret the question as a suggestion.