You're experiencing market segmentation. You won't pay $8.99 a month, so you don't get an ad-free product like the people who will pay. The service would rather get less than $8.99 from you than nothing, so you get ads.

But the part they seem to miss (or I get lost in the statistics) is that I wont use the service if I get annoyed by the ads. So they turn me into a churn which I wouldnt have been.