Most ad sales platforms have auctions for ad slots and/or keywords. If you want to game the system and have money to burn as growth hacking, you can place a larger value in those auctions/keywords to win a chance at your ad being placed in front of more eyeballs. When it comes to apps/games especially, people will chose whatever is posted from laziness, fomo, or just tired of looking and picking the easy route. I suspect that when you get an unrelated ad to your search, it's because someone else was willing to spend more money for those search terms than someone with more relevant matches. It's always going to be about those Benjamins.