A factory assembly job pays more than a management position?
Fast food/retail managers don't make that much unless you're a department/store manager. I was an assistant manager at Target in the warehouse and I only made $13/hour, and that is after working for several years worth of raises and $1 extra per hour for working overnights. Once you move up to department manager, you make good money, but it's salaried, so it ends up being not that great because you will end up working a lot of 50-60 hour weeks or more.
Even basic factory jobs can pay very well, especially if they are union positions. One of my friends went to the Ford plant after high school and made $20+ and hour off the bat (and that was back in the early 1990s). And if you work overtime, you get time and a half. The issue is (like the OP said) most of the jobs are basically doing the same thing hundreds of times a day standing in exactly the same spot. And of course now a lot of those sorts of jobs are gone - my friend got laid off with thousands of others when the plant closed and basically had to reboot his whole job path.