I honestly do not know :-/
Do you know why you can't breathe through your nose?
Maybe its how my mouth is arched. Or why my teeth are too crooked
Is that your guess, or the 'verdict' of doctors?
Some people just don't have functional nasal airways. It's blocked with body tissue. Sometimes that can be operated. And after that comes the exercise to learn to use those new airways.
Might be worth looking into, visiting an ENT specialist.