In your warehouse example, both guys are being paid hourly, but the forklift license holder makes more, because he is clearly both more productive and more skilled.
Are you sure? Anyone can shift boxes by hand it requires no training or experience whatsoever. Whereas operating a forklift is a skill that you have to be trained in and are tested on.
Also increased responsibility. You can seriously injure or kill someone with a forklift (I’ve seen someone drive the forks through the side of a fully loaded Cisco router once...)
Because you want to be highly paid?
In your warehouse example, both guys are being paid hourly, but the forklift license holder makes more, because he is clearly both more productive and more skilled.