They have more views, more data, more data that needs to be kept in sync across multiple views. You cannot rerender (and inject/replace) every time the underlying data changes. It works up to a point but once you cross that rubicon it because very painful. I don't know how better to say this or explain it. I write webapps professionally and for side-projects, maintaining any of them in vanilla js would be a non-starter. I have even tried that for "smaller" webapps that "don't need a build step", it doesn't work. SCSS is vastly superior to CSS, TS is superior to JS, and templates that support things like `v-for="item of items"` or `v-if="condition"` or `@click="doTheThing"` are superior to HTML templates with event handlers, loops spitting out html, and conditional rendering of blocks.
> You mean like generating forms/controls ?
Yes. Those things make this all more complicated. I've built exactly what you have in the past and at a certain point it falls down hard. There is a noticeable lag when you change data and go to re-render. If the user is focused on an input and you re-render they lose focus unless you make sure to reset the focus after the render. If you wanted to do something like "As the user types re-render an element to show what they typed" (think example/preview, or even something like putting the name you are typing into the UI as a header) it gets really gross really fast. So you might start having smaller render areas "I'll just re-render this 1 part" but that also gets complicated very quickly and at the end of the day you are just building a worse framework without the benefit of the community.