Actually I do. Whenever I need a small tool like a calculator for a video game or a simple GUI program for processing images, I always go for a barebones single html file web application.

For example, this is a simple visualizer for different numerical integrators that I wrote in a day or two for a college course: https://scleox.github.io/integrator-visualizer/index.html. The the source code is just one single html file: https://github.com/SCLeoX/integrator-visualizer/blob/master/...

That way doesn't scale well. Things become very messy and unmaintainable really quickly. This is how people code in the past, and there are good reasons why people moved on.

Code becomes unmaintainable when it was organized poorly and grows or if discipline was not maintained during growth.

React projects are just as susceptible to that, and "modern" web development is quite frankly a larger maintainability headache due to the dependency hell they bring.