If you have wealth, you can essentially create an income, on paper, to look like whatever you want, to meet ACA subsidy qualifications. Here's an example of a practical application: You could rent, or buy a home with your wealth. If you buy a home outright, you won't have the monthly mortgage or rental payment (you'll have property taxes, but let's assume those are far lower than an ongoing monthly rent check).

Withdrawing from pre-tax retirement accounts counts as income for ACA purposes. You've now lowered your annual expenses (and thus, your income) and can qualify for subsidies, but all you've really done is shift some of your net worth from investment accounts to housing, in order to reduce annual expenses. This example is likely more applicable to a person in retirement, as well.