Red T-Bar. It is a cost. Night flying attracts extra credits. Pilots can be paxed up to 24 hours continuous tour of duty but if they operate they must get rest in a hotel. Hours operated count towards min crew rest/weekly/annual total requirements whilst hours paxed do not.
Offsetting the cost is the availability of premium seats. You'd have to talk to management about who comes out ahead.
I am not saying you don't have a point regarding getting experience. Years ago S/O's operated on all flights regardless of length. My first trip was a SYD-MEL-SYD and I actually learned a thing or two that helped later doing domestic flying. But those days have long gone.