Also probably why they are relatively big for a device of this size.

If you're designing for a specific airflow target, making the fans larger lets you make them quieter because they can spin slower than smaller fans while displacing the same amount of air.

That and there are two major chips, the R1 and M2, acting as distinct heat sources. I don't know if they would spin the fans up and down independently, but the two chips' heat output could differ over time.