Pieces of paper in big boxes work pretty well, especially when they are enclosed in a sealed envelope with return address information for verification in case of fraud accusations.
Having the return address information on voting envelopes is a simple way to destroy deniability. Now you can prove who voted X if you have access to the envelopes.
I would argue that the paper voting doesn't satisfy both conditions either. And while putting a paper in a box is vividly understandable to the average voter, whatever happens to the vote after that point isn't, as evident by the number of people believing that a Texas lawsuit may overturn Michigan election results.
That's because there's video evidence of Fulton County Georgia poll workers clearing out all poll watchers on the basis of a bullshit pipe leak story and then as soon as everyone left they brought out suitcases of ballots and started scanning them in. There's 1000 affidavits of egregious election fraud and abuse in this election. The Supreme Court's refusal to even hear Texas's case is outrageous.