Amazon is promoting items that likely generate more percentage profit for them. Items that have lower fulfilment, higher profit margin. Higher selling price. It is likely they are also trying to maintain high demand items / thresholds as well. I am seeing a lot of items that are like in the 14-60$ range that were just never very popular and Amazon is suggesting these. Meanwhile my moderately priced items below 10$ only has like 4 skus in our inventory over nearly 1000. Its clear bias towards items that are most profitable for Amazon.
I have a product priced at 7.99. I am selling 60+ units a day through FBM. Amazon deems this non essential though, I assume because of the price point.