But CSS can easily restyle every baseline HTML element. Making the web page look like the product is not only entirely possible without having to layer a framework on top, it's likely often easier and faster to implement than layering a framework on top.
I heard dropdowns and certain some other elements are notoriously difficult to style. People resorting to tricks and js to handle their visuals. And it seems to be enough hassle to deem HTML+CSS a non-solution for some folks.
In short almost everyone wants their website to be a video game.