Grammar question

I like your point. The person rendering the quote in print knows whether it is upward inflected at the end, and conveys that in the only way possible, by the choices of punctuation

“Because” nearly always functions as some form of a conjunction, with a complete sentence before and after it. Either of those sentences can be a questions.

A comma often provides a valuable clue. “Did she call you because you are her cousin?” is quite different from "“Did she call you, because you are her cousin?” The first one implies a reason for a call that took place, the second asks if a call took place. The second one might not take a question mark.

It’s interesting to note that “He is reading this?” can be multiple different questions, based on how words are emphasized:
HE is reading this?
He IS reading this?
He is READING this?
He is reading THIS?
HE is reading THIS?
etc.