What can be done about this? It's simple but not easy. Do your best to encourage the people you know who like your movie to write a review on Amazon. Remind them that this feedback doesn't need to be eloquent. Of course, it should be genuine but it can also be as simple as "good movie." The important thing is to encourage the admirers of your film to take action.
These days, it isn't enough to have one good poster. In the streaming arena, the competition is vast; there are endless movies and TV shows to choose from. This means that the "key art" you choose to represent your film should not only be enticing (both in large form and as a thumbnail) but it should also be dynamic.