We like to see MathJax used on Physics SE for equations, but at present when you are typing in a new question I think there is no on-screen link to the MathJax "guide" or a reminder to use MathJax for equations.
There is an old Q&A on Physics Meta which says that this has been implemented, but it's not there now so must have been removed during site updates.
It might help to have something like this added to the new question edit page:
- Please use MathJax for equations in questions.
On Physics SE this would ideally be prominently above the edit box in bold maybe.
Certainly if we don't even mention MathJax to new users until after they've posted we're just asking for having to repeat the same thing in comments over and over.