I don’t think the issue is describing the gap, rather that “unskilled labor” has long been used with the implication that, since it doesn’t require extensive training or education to perform at a satisfactory level, the people doing this work are unworthy of receiving decent working conditions or compensation.

There’s also a tendency to negate the contribution of so-called unskilled workers to enabling more prestigious professions to exist. That a surgeon could learn how to do the janitor’s job to a satisfactory level doesn’t change the fact that without agricultural laborers breaking their backs to grow the food they eat, construction workers paving roads or laying out transportation infrastructure they use to get around, or the janitor keeping the hospital from becoming a filthy health hazard, the surgeon could not do their jobs. This atomized view of labor ignores the reality of interdependence between countless jobs to allow society to continue functioning as it does, obfuscating the indispensability of low prestige jobs in order to allow other individuals the time and resources needed to be able to train for and perform higher prestige jobs without having to spend an inordinate amount of their time attending to more fundamental needs like food and shelter.

In no society do you see surgeons, computer programmers, or engineers emerge and begin carrying out their functions without a far greater number of people first doing the heavy lifting of performing these less prestigious jobs. They are fundamental to our society, yet the label unskilled labor is used to minimize this so that people are more liable to tolerate the abuse and degrading conditions those who work these jobs are subjected to.