"lower side of income" means they are roughly linked to minimum wage. For instance, when I worked at a gas station as a kid, I explicitly got a wage $1 more per hour than minimum wage. Even if it's not so explicitly linked, the implicit link is there on all low end hourly jobs. If a wage goes from significantly above minimum wage to just barely above minimum wage due to a minimum wage change and the employer doesn't raise to match, they are going to have retention and recruitment troubles.
