They merely want the tax money.
Babysitters and single moms can be taxed. Mothers cannot. Have to convert all work to taxable revenue.
It remains weird that the IRS has so much pull when tax money is irrelevant to funding budgets. And yet, nevertheless.
Immigration is similar. Can't tax Mexicans. Bring them to America, where even the illegals pay sales tax.
Maybe that's why they hate lemonade stands, come to think. Too decentralized to tax. See also: optics of tax goons cracking down on 6-year-olds. It's not that they have any sympathy for children. Quite the contrary, which is why lemonade stands are de facto illegal.