They could tactfully include ads, but no one ever tactfully includes ads.
Because they don't work outside of basically podcasting. And even then many shows stretch "tactfully."
Additionally, over 60% of American internet users use an adblocker. The Atlantic as a US publication relies heavily on US citizens. They didn't create that situation, but they have to experience the ramifications.
So "tactful" ads are not an option. You don't want obtrusive ads that unfortunately are the only ones that vaguely work. You don't want to pay for it directly. If they went government funded or something it would be used as a cudgel against them forever (look at how NPR gets shit on it randomly, which basically gets a fraction of its funding from government grants and not even formally from the US budget). So functionally no ads, no selling, no subscriptions, no government funding.