why would someone hire a WordPress developer?
It is really easy to do a WordPress site with themes and plugins. And that is the big problem. That makes it really easy to do a bad WordPress website.
It comes down to lack of training. If someone is not in marketing or web design or that person has no graphic design skills, content marketing knowledge, or understand SEO then how do they know how to create a site for their business that is going to not only be effective to get visitors but also be effective in converting them into customers.
I have seen some very poorly done sites. Using a theme makes little difference since customizing themes is not easy. It is not easy to set up and design the site, even with a theme, that reflects a brand with the degree of professionalism needed to have a visitor trust the site enough to want to do business with them.