Sometimes, your business demands an e-commerce store that has very unique needs.

Sometimes you need something small that can be easily managed using a solution like Magento or OpenCart. And at the other end of the spectrum, you might need custom development from ground up.

Off the shelf, readymade solutions have other issues too, like

Being too simple or too complicated for your needs

Technically unfeasible because there is too much product data to migrate from a legacy platform. Being too resource hungry with massive load on the servers.

Having cumbersome indexing rules which prevent new products from showing up hours after they have been added to the database.