AdWords rewards advertisers who choose relevant keywords and write compelling ads with good Quality Scores. The better your Quality Scores, the less you'll need to pay for each click, resulting in more profits for you. This ecosystem evolved to benefit users, Google, and advertisers. If the ads on Google were irrelevant and of poor quality, users would get frustrated and not click on them, and Google would lose revenue. From an advertiser's perspective, when users click on irrelevant ads, they tend to leave your website, costing you money and not contributing to your bottom line. AdWords was designed to encourage high-quality ads, and as an advertiser you'll reap many benefits from optimizing them to improve relevance.