The issue is that there is no such uniform amount.
If your spouse makes 85% as much as the two of you need to live with dignity, you don't need to make as much as they do and may prefer not to because the lower-paying job is less difficult or more satisfying. For someone else it could be 95%, or 99%, or 250% and the second job is pure supplemental income, so what's the minimum meant to be here?
The minimum wage doesn't account for costs. A job across the street from you means you don't need a car, don't have to pay for fuel or maintenance or transit tickets and don't have to spend hours in traffic (which you could have spent working and getting paid). For a long commute this difference in value can be more than the entire minimum wage.
It's possible for jobs to provide training, which is attractive for entry-level workers or anyone trying to change occupations or learn new skills, because school otherwise costs money. But if you're spending extra hours "at work" getting trained while the value of the training comes out of your paycheck, there isn't any sensible "minimum wage" for this. You could be receiving $50,000/year worth of training while "getting paid" only $5000/year and you're the one coming out ahead because you don't otherwise qualify for a job that pays $55,000/year. You might still be ahead if you were paying them $5000/year.
So how are you supposed to set a minimum wage if the "minimum amount required to live peacefully and with dignity" is different for everyone, and setting it below that threshold deprives people of valuable alternatives?