Why does the heat only blow from the dash vents and no where else?

There are electronic motors that control doors within the dash. The gears inside the actuators are plastic and over time they wear out, break or the motor goes out. Depending on if you have dual controls, one for driver and passenger you may have more of these acctuator motors. Some are easy to get to and some are where you have to dismantle part of the dash. Sometimes I have seen people remove them and open them up and regressed them with white lithium grease and they work fine for years before needing to be replaced.