Why Airline Seat Maps Only Show Bad Seats

I regularly check availability for upcoming flights (I usually have 3-4 weeks of flights booked) and additional seats regularly become available. Plenty of Preferred (i.e., pay for) seats are always available, but the normal exit, aisle, etc., that I look for trickle there way in over time. I would be surprised is passengers are giving up aisle/exit seats on that regular a basis, and I have status with the airlines I travel.

I'm not a big-bag-airline consipracy fan, but it seems clear they are managing the seats that are available to encourage passengers to take revenue-generating seats.