The updates are handled by JavaScript and http calls.
You can write a lot of that stuff in a dozen lines of JQuery with nicely refreshing content and ajax instead of throwing in large amounts of framework bloat.
OTOH jquery is much bigger than you'd expect, there isn't much of a difference between a minimized jquery and vue, or even react once you factored in gzip.
And while I've no experience doing so using vue, writing small dynamic react components embedded in larger static HTML pages is quite enjoyable.
When you have 2mb worth of "React code" and the framework itself only takes up 35.6kb, that's a lot of bloat.
And if the project isn't worrying about bundle size at all, then even their vanilla/jquery page is going to end up bloating a ton as well.
More often than not the culprit in 2mb bundle sizes is a a few packages that include "data" in the bundle (For example, i've seen timezone and locale information bloat bundles by megabytes, and in one case a 5mb bundle ended up being 4.6mb of zip codes...)
Even ignoring that, React app sizes are getting better. Modern React apps (basically since 16.7) that are written with things like Suspense, lazy, and hooks are usually pretty small. Writing functional components and composing your app pushes you to write less code. Plus React gets things like code splitting for free with webpack if you use lazy, so the first page load only downloads things that are actually needed to get to interactive.
No doubt some less considerate developers will still manage to write giant apps that take ages to get started, but they don't have to. Bloated apps are a function of developer's choices rather than React (or any other JS framework) forcing the apps to be bloated.
