I've never signed up for Google AdSense.
I simply enjoy writing and reading items on HP. I also write for Examiner.com which has more of a process to become accepted as a writer. However once you are accepted you do not have any dealings with a third party such a Google.
Having said that the purpose of launching a website or forum is to generate income from advertisers. The owner of the site informs advertisers exactly how many clicks and views they get daily as well as the typical readers age/income demographics. Writers who write for profit realize they get paid based upon the number of times their articles are clicked on or read.
In most instances both the owners of the site and the writers want to increase their revenues/incomes above all else.
It's a balancing act to maintain quality/reputation and popularity. Generally speaking the writers who are the most social media savvy and have a network of contacts, followers, or fans that read their postings regularly and whose articles are frequently highlighted/promoted by the site will earn the most.