Being a mouth breather has a lot to do with being around car and truck traffic. I commuted on I-75 for a very long time. Only after moving to the country did my nose breathing take over. If I get behind a diesel truck now for even a few seconds I feel my nasal passage changing.
There was a major positive change to air quality years ago after low sulfur diesel was introduced to the trucking industry.
Or in my case allergies. I’m congested a lot of the time (even with meds) unless I’m taking allergy shots and even while taking allergy shots