traders can't open a Roth IRA because they have no earned income
Not necessarily true -- by using entities and a management fee, you can have earned income, as well as numerous other advantages such as tax-advantaged health care payouts. But don't take my word for it as I am not a CPA -- see e.g. Green Trader Tax's Web site.
https://www.lightspeed.com/active-trading-blog/entities-provide-tax-benefits-traders/