You’d presumably be happier if they got monies and you didn’t have to see ads. If you’re not intending on acting on the ads, the end result is the same. It’s just you have to give up some of your time. You’re paying a middleman with your time (which is not worthless, I hope) and they’re paying Ecosia. The people advertising their product spend money and don’t get anything in return from you, so it’s difficult to present this as a system that would make sense to any outsider.