good question.
Actually , to understand the situation we should go to deep level I mean at that level so that we can think why we want to create the Ecommerce website, the question is so simple and answer would be very simple that one who is in an Ecommerce business will also develop an ecommerce website
The businessman wants to grow its bussiness either online or the other way
There is a well known saying What is seen is what is sold
so in E commerce website, there is a slight different SEO purpose..
The purpose is to increasing the sales of the product by marketing , advertising etc
So that's why you should take Ecommerce SEO with a different Approach..
Thanks