A long time ago my uncle told me about his supervisor questioning another employee. The supervisor asked his coworker why he only worked 4 days a week. His response, because he couldn't live on 3 days pay. It's all about perspective.
There are UPS drivers in mcmansions, there are UPS drivers in doublewide trailers. If they can perform the job a few days a week they obviously have the drive inside to work at the pace we are required to work at...Most of the young people at my building would quit before they ever got qualified...Too much work. So I guess these guys have made the decision to prioritize other things in life.
They may also be smart and taking it easy since they are still in progression. Why kill yourself to make $1300 gross a week when a few years from now it will be $2500 for the same amount of work?
I would gladly work a few extra years later in life in order to spend real time with my children while they are younger. They are my priority at this time in my life and I am thankful/happy to be on call in feeders at this point because my schedule is flexible.