Part of the issue might be sitting in the car too long after shutting it off.
My GF has this habit, she'll park, turn off the car, then spend a minute or so getting stuff in her purse, etc. before exiting the car.
Sitting there with the car off means no fresh air through the vents which means all the moisture you exhale stays in the car.
Also, snow melting off your shoes collects in the mats. These only dry out if you go on a long drive (an hour or more?) so if you're doing a lot of short trips it will collect there and add humidity.