If your goods are placed in Amazon's FBA warehouse but do not sell well, Amazon will charge you an obsolete inventory fee (formerly: long-term storage fee) after it has been left for a period of time.
In recent years, Amazon's sellers have been growing very fast. Most sellers will put their goods in FBA warehouses for shipment. Therefore, Amazon's warehouses are full of stocks in the peak season, and once the goods are sold out, they cannot get in. Your goods may have arrived but have not been successfully warehoused after 1-2 months. In order to solve the problem, Amazon started charging obsolete inventory fees.