Here are some examples of incorrectly set up feeds. In the next picture you can see that only a snippet from each blog post is in the feed, so no links (so the system can't see if there are freebies) and no images (so even if the system found a freebie there are no preview images it can use):
Here is a secont example. Here, the next picture is the blog post containing a freebie and you can see the preview image, and a download image which contains the download link to the freebie below the preview.
But the next image is what the feed looks like - notice that the download link is now missing? A system will look at this and not pick up that there is a freebie contained here. The word "freebie" in the title alone is not enough - people mention freebies all the time for lots of other reasons.