Do people lose interest in TeX/LaTeX after leaving academia?

In my case yes, because back in the 90s I had to write Word files at work, when I had to write something. More recently because I write inside any tool my customers are using and in md files for myself.

Obviously none of my customers nor myself are writing academic papers. If we did maybe we would be using LaTeX, but the chances to have to write papers in normal companies are slim.

I used LaTeX extensively at uni for my BSc/MSc then took a 30Y+ break to earn a living, now I am back using LaTeX for journal papers for my PhD.

I didn't stop caring about good typography and typesetting, eg I edited a supercomputing trade rag for a while.

And I don't like flaky WYSIWYG editors, so have preferred (say) HTML over Word for most of my text output.

But I just didn't have cause to use LaTeX or maintain that toolchain for decades away from academia, so I didn't.

I have only used it for academic papers, which I still do every so often, so I would the answer is mostly yes. I tried using beamer for presentations but it was too much effort for not enough gain. I use tikz for diagrams and graphs in academic papers, really useful for updating graphs by just ruining a single script. But outside of that, again, it was too much effort for not enough gain, when I can just print out jupyter lab output..

Pretty much, I only care about typography when it comes to academic papers, so that’s the issue. If I care about it in other contexts, I probably would use latex.

Still writing all my letters with LaTeX (using DINBrief).

If high-quality typography is so important why are web pages so prevalent?

I think so, at least for myself. I think this is a habit formed with conventions, industry has its own conventions different from academia and more driven by productivity and ROIs.