I don’t personally know all the designers and developers who are cranking out the hundreds of themes on ThemeForest, but I can tell you on thing about them:
They don’t know how to size a font.
Eyestrain is the #2 reason why people abandon a website after a Google search. The number one reason is that the page doesn’t appear to answer their question or cover their specific point of interest. The number two reason is that the site is hard to read.
If you’re designing a static website that is never going to change, smaller font sizes are forgivable, though far from optimal. You want to look professional, and you think that large fonts are like handwritten fonts, i.e. unprofessional. And you might be right. Perhaps larger, easy-to-read fonts are casual. But they’re also effective. And enjoyable. And easy to read.
So before you design your next premium WordPress theme, or purchase from your favorite online store, consider the user experience. Ease of use = success. Difficult = lost opportunity.
Do the math.