supply and demand. flipping burgers has no gatekeepers, natural or artificial, and lots of people are overall willing to do it, so workers are easy to replace and wages can be pushed down a lot. there are low skill jobs that are actually well-paid, but they usually involve way less savory stuff that fewer people like to do.

of course, if a strong social safety net, or heavens forbid, universal basic income happened, way fewer people would be willing to flip burgers, while the demand for burgers would likely go up slightly, so people flipping burgers would get paid better, because a lot fewer people would want to flip burgers. hence the comparisons to the good half of europe where people flipping burgers get paid better.

but the point is, when a job is easier to do, it's because it's gatekept in a way that some harder jobs aren't. sometimes that's due to skill, other times it's entirely artificial. but a gatekept job can't be a universal "hey, do that job instead" thing, specifically because it's gatekept.

ubi would be great because it would make it disproportionately more difficult to hire for hard jobs than for easy ones, but when the alternative is starving to death, a lot of people accept the hard job instead.