The problem is those jobs aren't worth more than that. They aren't meant to be family-sustaining positions. Hey, I want a job raking sand traps at my local golf course but they aren't gonna pay me more than $8 an hour either because you know what? At the end of the day, nobody needs a sand trap raked. They are only going to pay me based on what they calculate I am bringing profit to them, and that's based on, hey, we only need that sandtrap raked like, twice a day.
The cashier at Walmart isn't generating that company enough revenue more than what they are getting paid. If Walmart paid everyone more, the company might start losing money. This is a myth of wealth accumulation. Say I make 1 penny on every transaction, and I make that transaction a hundred million billion times. Well, I'm gonna have a lot of pennies, meaning a lot of money. But if I increase my costs just 2 cents, now I lose a penny on every transaction and I'm no longer profitable, and in the same number of transactions, I'd be staggeringly in debt. Walmart may be fantastically successful without being in a position to raise their costs tremendously, if they operate on razor thin profit margins.
You want more money? Add more value to your company.
Very few reasonably educated, reasonably motivated people can't figure out how to do that.