Ask HN: What is up with "Offer HN"

Why arnt these Offer HN posts deleted? I thought HN was supposed to have links/comments that are deeply interesting and provoke thought. Wont an excess number of these posts, which have spam-like tone, turn HN into a tech Craigslist? Whats next: Offer HN: Great work at home opportunity, make $1000+ a week!