They're essential, but they're also numerous. The barrier to entry for a lot of these jobs is "went to school for some time" - which means pretty much everyone is qualified.
Supply and demand.
Notice how when service staff were allowed back to work, a lot of them didn't, and that drove up zone wages.
And to be clear - I am not advocating for below living wages, nor saying that people doing these jobs are unskilled. You can tell the good from the bad, and I think everyone should be paid at least a living wage.