What is the point of single page large applications if you have to split your code to improve performance?

I've been reading about lazily loading code in react.

With lazy loading, only the needed code will be loaded and doing so, your initial loading will be faster (because you will load much less code) and your overall speed will be much faster being on demand.

This is what I've understood. In a single page application, the entire page is loaded onto the browser initially. We use module bundlers like webpack to bundle the application into a single page. Everything's great. Now, if the application size is large, the load time would increase. To improve performance, we can divide the bundle into separate chunks that will be loaded only when needed. My question is, if we have to divide our page into chunks, is it still a single page application because the browser will have to request the server for these chunks whenever they are needed? I feel like there's a gap in my knowledge and I don't know what's missing.

The traditional web applications used to work with postbacks to the server to fetch HTML to render a new page. Then AJAX came into the picture and applications were able to render data asynchronously thereby making sure that the user doesn't need to wait the time when the browser would refresh on postback to render the new page.
Modern Javascript libraries like angular, react etc. bring single-page application (SPA) model which runs inside a single page without requiring the browser to reload as the user navigates the site (ie. with only a single container page for entire application,like index.html). Even with code splitting and lazy loading of chunks, the application developer can ensure that user gets a pleasant experience like displaying a progress bar or loading spinner instead ( using React Suspense ). This is much better than the frustrating experience of waiting for a page reloading everytime.
Webpack ensures the chunkhash changes only for chunks which have changes in source code from previous build. This helps to take advantage of browser caching so that the request for chunks don't need to go to server everytime. Hope this was helpful !