JS frameworks have often valued DX first over what it outputs. Frontend devs also frequently care more about a) their own tooling and b) how it looks, to a much higher priority than the performance and stability of their output. At least from my own experience in the community :)

Oh my god, yes this is hitting the nail on the head in a way I hadn't thought before. The bloat comes from the discipline (or lack of) more than the framework.

IMO, those who have only worked in React tend to be unfamiliar with the layers of native capability that React is built upon, and so they are stuck in the React bubble unless they want to learn a ton of (admittedly crufty, but useful) web fundamentals.