Common sense is very uncommon :-).
E-commerce stores are not easy as business, but very easy to launch today because technology is the easiest part of it. The biggest difficulty is getting traffic, then conversion to order, then with superior products, logistics and customer service retain the customer. No one can setup logistics, product catalogs, superior customer service from day 0, it takes quite a time and feedback loop. So remember in the grand scheme of ecommerce store for merchant time taken to build or launch a system is minuscule compared to other hard physical world problems they need to solve around products and services they are offering.
Today literally thousands of options are available to launch an ecommerce store with single click with better quality, speed, flexibility and control than shopify.
Shopify is just one another provider with walled gardens. Shopify is popular not due to any innovation in technology or quality or speed, its popular because it spend literally billions of dollars of investor money in marketing. So they succeeded by throwing marketing money, not due to innovative technology.