I think there's a logical explanation for this. Low skill jobs tend to have an oversupply of labor, relative to demand, so wages are going to hover around the cost of basic living. But as that cost of basic living skyrockets, wages are going to be naturally pushed up - simply because workers cannot afford to work for less.

But for higher wage earners basic cost of living expenses (food/energy/rent/etc) make up a smaller percent of their overall income, and so they are relatively less affected. And if they don't aggressively demand their pay keep up with inflation then their relative rate of gain will naturally fall behind.