One should note that the cited study quotes the 45% from a 1992 study. These days, with gig economy and quasi-self-employment, that number is probably higher since you don't have an employer who reports your income for you.
Still, here in Australia, where we have the return-free tax system, adding what you earned from your various gig jobs isn't too hard: you add that as items to the web form: 'I made 15,123 from Uber Eats'. That just gets added to your overall return. I don't see how that's so hard compared to the US?