> I have no idea in what reality you live where you encounter SPAs of a few Kbs. Don’t even know what to say if that’s your experience.
Let's look at a SPA version of HN [1] and compare it against base HN. This base SPA page fetches 21 KiB of data. The base version of HN fetches 36 KiB of data. Most SPAs are much less information dense and have a lot more CSS and media than non-SPA websites. In a world without SPAs these sites would not be leaner, they would instead just insert tons of CSS style links and img tags to fetch the media themselves, resulting in the same amount of bandwidth.
If your argument is that websites should be leaner regardless, well in my experience most users would rather put up with a slow good-looking page than a fast spartan one. It's a hallmark of a nerd that's willing to cut corners just to get access to the information they want.
[1]: https://hn.premii.com/