The irritating thing is that this is often possible even with modern JS. I shipped a rather complex app (though still essentially CRUD that's used internally) this winter that is Vue 3 based. It's just the Vue library itself plus the app logic, directly included using script tags. No other libraries for Vue, no build steps and so on.

It just feels great that I could just immediately start fixing things on any computer should an issue pop up next year or so, without worrying about dependencies or some build step being broken etc.