Why are ads disabled on Amazon for hubs that pertain to a specific topic that Amazon sells?

The short answer is just because Amazon sells an item it doesn't mean that HP will let you publish hubs (or hubs with ads) related to the item.

Amazon sells everthing under the sun because they make money primarily by selling items, not running ads. (Although they do seem to run a few ads.) HP makes money solely through advertisements, and advertisers like Google Adsense have their own strict polices about what kind of content can support their ads.

Actually though, HP's content guidelines are much stricter than Google Adsense's, because you can find many websites that deal with domestic violence and run Adsense.

You should probably contact HP and see if a moderator will override the automatic content filters. Good luck.