React is quite a minimal framework (or not even a framework), actually. It's just that it has a huge following and takes some mind-bending to actually benefit from it.
In most cases, at least one of those is not true and the developers are using something like CRA so your site has a number of users who see tens of seconds of nothing while their Android phone downloads and runs a 1MB JS bundle. Bonus points if the marketing department has tossed in a tag manager which delays that even longer.
Working with any significant backend API, loading any images, or even your own javascript functionality takes you over that limit easily.
And then there is caching and CDNs...
A 100-lb gorilla is...quite minimal, actually.