Storage is just too expensive. After a while, with multiple areas unlocked and a largish main city, there's just too many products, all are required for upgrading building, but the micro managing of products and storage space, being forced to sell stuff you know you'll need later, just becomes too tedious. And expanding the storage at some point is so expensive, and especially that you need to clear space to store the stuff you need for the upgrade. Fun for a while, but I quit playing specifically for this reason