That's not true in NYC, food service workers have a minimum wage of $15. other groups you're thinking of also have minimum wages (i.e. door dash drivers)

the labor force participation percentage is a slight of hand. You're including children (who receive free metro cards), retirees (including social security beneficiaries, pensions), and people who might just be rich. 40% has nothing to do with people's ability to make or have money.