How to Add AdSense to Restricted Sites?

[mattbop]

I cannot understand this. We can see advertisements stating "Adsense account for sale" on websites that download movies, games, and mobile apps, as well as on sites sharing explicit content like +18 content. These accounts are being sold until the buyer gets banned, and profits can be made until then. How are people able to do this? Does Google not understand and ban these accounts immediately, or what is the timeframe for getting banned? I am awaiting comments, suggestions, and opinions from friends who know about this.