One fan might not be enough for the amount of heat generated. The airflow engineering could be very poor, requiring high velocity and not just high cfm to overc

One fan might not be enough for the amount of heat generated. The airflow engineering could be very poor, requiring high velocity and not just high cfm to overcome. It could be positioned poorly or attached to a skimpy heatsink to save on copper (or even worse, to save on another metal). The hottest components may have very small surface area so they don’t diffuse heat efficiently. Lots of reasons, usually having to do with thermal engineering not being a priority until late in the game.