My new gig is to clean up the mess left behind by a now ex-development team that insisted the company would be better off with a custom-coded ecommerce solution that completely disregarded the conveniences and ready-made plugins provided by the CMS (Wordpress). They didn't even bother making a plugin. Just mixed the shopping cart scripts right into the theme files. Why are there coders who insist on doing such things? If you are one, what is the benefit you see in taking such a "custom", unconventional approach (other than locking the client into your solutions)?

The theme files of this WordPress site I'm supposed to improve are completely and unnecessarily custom for a simple ecommerce site. I'm really regretting not spending some free time I had recently to better learn plugin programming to abstract out this functionality for this customer.

Which is the best and affordable eCommerce theme? I am looking for an eCommerce theme for my online fashion store.