There are a lot of things you can do with WooCommerce and a server you could never do with Amazon Seller accounts, and from what I remember, Shopify. The plugins developed for WooCommerce tend to reflect business needs...something you won't find support for with closed systems or hired developers necessarily. We've seen our sales grow over 100%+ since moving to WordPress- largely thanks to our ability to control the UX and use plugins to improve the customer journey. If they're not talking about it at a marketing conference oh well.