I suppose it depends on a lot of things. My personal viewpoint is neurological. My brain and body dont work well in slow moving jobs, especially if they have surprise „hurry up and wait“ situations.
The other problem is that where I live you get fired if you read on the job, no matter if you dont have any work for 6 out of 8 hrs. You‘re supposed to get busy or at least look busy.
Thats why I usually work self employed. I can decide what to do with my time. I usually work a lot more than 8 hrs and I expect to be paid for the work I do, not the minimum required amount I am owed.