[edwcross]

Could it be for driver comfort? I sometimes have the impression that buses have their temperature tuned for the driver, who's staying in the bus for hours and has everyone's safety at least partially related to their comfort. But I find it impossible to confirm this by asking the bus companies why their buses are set this way (e.g. when windows were closed during Covid at about 20°C).

[Fatnino]

The bus company doesn't set the temperature, the individual drivers do. That should explain everything.