Does the subject want to ask "Why don't you do it?"? Whydonotyou is followed by verb prototype, verb phrase and noun.

1, verb prototype: This is the most commonly used form to suggest that the other party take some action, for example, why don't you go to the park.

Verb phrase: In order to explain the proposal more specifically, you can use verb phrases, for example, why don't you go running?

3. Nouns: In order to give more specific suggestions, you can use nouns, for example, why don't you try a new recipe.

4. Verb prototype refers to the basic form of verbs, that is, verbs with no change in tense, voice and mood. In English, verb prototypes are used to express suggestions, commands, requests, etc. It is a form in grammar.