They either start their own company/contracting, become highly specialized professionals, or get a degree and take some boring white collar job that pays better.
Managing finances is just a gimmick when you have zero disposable income. That's basically 24/7/365 crisis management.
Sure, if you manage to get some savings/credit-score together it's very important what you spend it on. (Eg classes/moving or finally doing that trip to Vegas you always dreamed about.) But if you can't increase your income significantly, then investing or spending it makes no difference. (Because investing it is just continuing the saving, for whatever purpose, let's say to have a rainy day fund, or medical emergency fund, amd spending it just decreases the years you spent saving up, but your overall lifetime income will not change much, thus your range of possibilities won't either.)