I suspect a couple that only earns $30K a year probably pays zero, or close to zero, federal income tax. The standard deduction was close to $25K in 2020. So their AGI would be very low. If they have children they likely receive a number of refundable tax credits. Meaning they probably get a larger tax refund than they had deducted in taxes.
I think the issue here is that people seem to expect low skill introductory jobs to be a career and thus should earn a living wage. However "living wage" is defined. That wasn't really the intention. Should you expect to work at McDonalds your entire life (unless you have management aspirations)? Outside of the current labor issues, what incentive does an employer have to hire a teenager wanting to get employment skills when they can instead hire an adult for the same price? That adult is likely to be more dependable and easier to schedule than a kid still in high school. Increasing minimum wage pushes even lower level workers out of the workforce. The true minimum wage is $0 when you have a mandatory minimum wage. Also, as previously mentioned, mandating higher wages puts the US at a competitive disadvantage globally. While automation may create other jobs, it certainly doesn't create enough to cover the losses in the lower level jobs, or companies wouldn't do it. Why create automation that isn't going to save you money because you are paying engeneers and programmers more to come up with the automation.