Vanilla css/js are not really that voluminous. Actually, they tend to be smaller than the compiled targets you get from conventional web dev builds.
I’m not really sure that most web frameworks reduce boilerplate. There is a lot of boilerplate involved in setting up routes, and builds, and so on. As far as I can tell they only really make sense for very large teams (who need a uniform shared data model, design language, processes, etc.) and people who really want to run server side js/do a lot of SSR.
The thing about web “frameworks” is that they’re not that different in structure from what you’d build to do SSR and a repeatable way to add pages/dirs and shared assets, in any language. You can build a minimal version of something that does that in less than an hour, at least in Go. go:embed and a factory method for handlers :)
I think we’ll all end up with more bespoke “frameworks” (specialized web servers) with less gravitational pull towards dysfunctional (IMO, the node ecosystem) tooling, and still have many people using the best major frameworks. Truly large projects will still need to use react and svelte and co unless they can train a model on their own framework. But that’s really hard