I work with a lot of kernel dev type people, you may find it hard to imagine but there are a lot of people that only program in c, maybe python.

I even know a lot of fortran only programmers. If you think html and css are common you might want to expand your scope of programmers, there is a lot of people that don't need or want to know about web programming.

I'll use my Father as an example. He works for Autodesk, before that he worked for Revit (when they were a tiny startup before Autodesk bought them out). He writes code in C++ mostly (I think some C# these days). He doesn't use HTML or CSS, and has never learned either. Not because he can't, just because there's not been any point and because the amount of effort that would take is large enough to not be worth it. Why spend several hours or days of extra effort just for a blog post? Not to mention the extra money needed to buy a domain and hosting.

I haven't touched HTML since somewhere around v. 3.x... I haven't ever bothered to really learn CSS. I am retired, but I once write software to model traffic.

Just another datapoint for you.

I can install Wordpress and a theme. I have no idea how to really customize said theme. I could learn, I am not feeling compelled to do so.