In our case there are no big companies involved. And Stripe, which we use, makes the payment as simple as possible for the user. It feels more like plain unwillingness to pay anything at all.

Can't say anything RE advertising. Don't have experience. But I think you’d need an even bigger user base to make ads meaningful. And I’m not even sure Trello would allow it. I’ve never seen any other plugin do that. Do you have an example?