Even though the job of construction flagger is an unskilled job, I think that these men and women should be paid more. This is a dangerous job - quite a few are either killed or badly injured by cars. They have to be out in the weather conditions all day. I don't know what kind of benefits, if any, they receive.
I'm surprised that their training course to earn their certificate is only one day long. That doesn't seem like enough time to learn the procedures well enough.
They probably have some confrontations with motorists who get belligerent and don't want to wait, so they take off to drive past the construction site. It's not an easy job.