There was a time around 2016 where you weren't allowed to write a React application without also writing a "Getting Started with React" blog post. Having trained on all of that, the AI probably thinks React is web development.

Tell claude to build a functional website using plain html and css and no frameworks and it'll do it in a second. Now try that with a junior dev.

Indeed, this has been one of the first things I've noticed

Few months ago I did exactly this. But over time I threw away all the generated js,css and html. It was unmaintenable mess. I finally chose Svelte and stuck with it. Now I have a codebase which makes sense to me.

I did asked AI to generate landing page. This gave me the initial headers, footers and styles that I used for my webapp but I threw away everything else.

Just write up your requirements in and AGENT.md, to avoid repeating yourself. It has worked really well for me on a PHP+Apache project.