Often performance issues are overlooked/underestimated. The fact is, performance is directly related to the conversion rate (revenue) of the site.
Several researches say when the performance is not good, a considerable number of users drop from using the site. Every second of improvement in load time decreases the bounce rate by 7-10%, increases conversion by 7-10%, and increases user engagement by 10%.
An Ecommerce site with good performance makes the users explore/navigate more pages, which in turn creates an opportunity to get orders from the users.