As for why some part timers don't want to drive.
Some are going to school
Some just need the insurance
Some just need extra money on the side
For me it comes down to a few things, even though the pay is great
1.) it's not fun being a new driver. You don't get your own route for quite a long time, you work longer hours than the other drivers, when you finish you have to help other drivers, your seniority is reset, you lose your vacation time, you're often laid off.
2.) you can't have facial hair. It seems silly, but can a guy really put a price on not being able to grow a beard their entire adult life?
3.)I enjoy loading trucks. Yup, it can be hard and the sups can be dumb, but loading trucks is kind of like a real life mini-game. Can be enjoyable, you don't have to talk to anyone, you can listen to music, you can say pretty much anything because there isn't any customer service.
4.). It's incredibly nice to ALWAYS get done at a certain time. Once the drivers are on, you can leave. Doesn't matter if you had the worst day ever and the trucks are a mess, you can go.
Edit: want to add that when you're part time sometimes you can work next to some pretty fun people and have a good time, while drivers are pretty much in isolation. Which can make it hard when you have to lift 150+ lb crates as well lol