Why? Because owner of that site had resources to do SEO (if one has money, one can trick Google algorithms without much trouble). How they earned that money? Through ads, obviously.
The more ads such site has, the more revenue comes in and more money can be spend on SEO to increase revenue. And so one.
Who pays for that? Those who landed on such site, they wasted time, read some potentially infomercial content.
This ads -> money -> SEO -> more ads -> money is not particularly beneficial for the economy. This looks like one more incarnation of Gresham-Copernicus law - bad content is pushing away good content. If you spend money on content, you don't spend them on SEO, so you earn less money from ads and finally you end up on 5th Google results page and that's the end.
A whole lot of news articles are just regurgitated Reuters or AP. There's nothing wrong with that and it is a valuable service. But I am completely indifferent to these sites existence.
The sites that I would really care about if they went under, like HN, Wikipedia, NYT, etc, either use subscriptions or are donation funded. HN has job ads but they are super low key.