Why aren't Maybe sentences questioned marked?

Maybe sentences that start with a question should end in a question mark, or maybe they shouldn’t?

Maybe I am a bowl of soup, maybe I’m not.

Is it the word shouldn’t that makes the first sentence a question? Both have the sane beckoning to question via indeterminacy, that implies a need to positively answer, even if sarcastic. You can answer if I’m a bowl of soup or not, even though a question mark isn’t presented at the end, and it looks correct just leaving a period.

Maybe. Maybe not?