Why not? Not everything in this world is about money. There is plenty of projects which are made for community to use which aren't commercial. But probably it's not worth to put much effort int website and don't get many visits, so probably this is why he decided to advertise. And as he said in one post, his budget is small, it means that he don't spend thousands of $ for advertising without getting revenue.
Though, persoanlly I would try monetize website to cover expenses at least partially, but he probably know what he is doing.