You have a point, but Ecosia strives to be carbon negative, including trying to compensate Bing's emissions (which Bing doesn't make clear how much is carbon neutral) [0]. And while you are right more users, even users that block all ads, is a good thing. If nothing else, being in the top 5 search engines in many countries assures Ecosia is present in Android's search engine choice screen [1].

[0] https://blog.ecosia.org/why-carbon-neutral-is-not-enough-eco...

[1] https://www.android.com/choicescreen/