I generally disagree with most of the arguments here, but the last part of this article makes a good point that the business owner (person buying website) usually doesn't make the decisions about the technology that gets used. This is especially true for SMBs (I'm excluding the DIY/hacker-types here).
I built a WordPress plugin inside of HubSpot called Leadin (it's now their HubSpot Marketing Free product). The idea was to build light weight marketing automation for Very Small Businesses. We started on WordPress because most small businesses use it. We incorrectly assumed in the beginning the business owners would be the decision makers on whether or not to use our product. We quickly found out it was usually the web development agency/consultant they worked with who would install it for them, then explain the value of the product. We eventually shifted our marketing to focus heavily on agencies which became our main acquisition source.
Agencies like to use WordPress because it's customizable enough to easily build what their clients need, is the same interface across every site and has a huge ecosystem of the add-ons that their clients what. Until you can replicate the WordPress 3rd party developer ecosystem it will remain the dominant player. Also, static sites can't do all the things WordPress does, like polling, comments, shopping carts, etc. you'd have to rely on a third party for those components and when you add up all those, I'd think that would be more than $100/year in subscriptions. It's easier and cheaper to have it all centralized in WordPress which is why agencies choose to use it. If you can charge a retainer too, the holy grail for agencies because it's reoccurring, predictable revenue, you're essentially getting paid to just keep things updated and make sure they don't break or get hacked.