Outdoor Thanksgiving decorations are more difficult to find than either Christmas decorations or Halloween decorations. The problem is timing. Thanksgiving in the United states falls after Halloween, and before Christmas. Stores commit shelf space to Halloween decorations, then replace them with Christmas decorations. There is simply little shelf space left for Thanksgiving decorations. It is, however, possible to find a variety of Thanksgiving decorations online.
The other problem is the nature of the holiday. It is a family event. The main focus is family, and there is often a shared feast. People do decorate indoors for small children to enjoy, or for a pleasant setting for the family gathering. But, there is no Thanksgiving season. The event is one-day long. And, in the United States it is too close to Christmas for extensive decorating. The Christmas decorations go up right after Thanksgiving, leaving little time to remove decorative items.