They're trapped - probably unable to even scrape together the money to move. Moving is expensive! You need the money not only to relocate, but also to tide you over until you find work. Casual mobility is for the wealthy.
It isn't just that, many low wage people have their families there. Sometimes extended family. Moving would mean moving the whole clan away from friends and their connections and where they grew up. Moving is not a small thing.
Exactly this. Moving elsewhere when your extended family has lived in one place for multiple generations is probably one of the largest risks a person can take. You’re essentially trading most or all of your network for the possibility of a better life. If the possibility doesn’t work out, the person is usually worse off than if had they stayed in their original location.
And no childcare for their children.
Not to mention that less wealthy people often rely on extended family for support such as childcare. For many people, leaving family behind is a risk not worth taking.