It is pretty established at this point that React has (relative) terrible performance. React isn't successful because it's a superior technology, it's successful despite being an inferior technology. It's just really difficult to beat an extremely established technology and React has a huge ecosystem, so many companies depend on it that the job market for it is huge, etc.

As to why it is slow, my knowledge is super up-to-date (haven't kept up that well with recent updates), but in general the idea is:

- The React runtime itself is 40 kB so before doing anything (before rendering in CSR or before hydrating in SSR) you need to download the runtime first.

- Most frameworks have moved on to use signals to manage state updates. When state change, observers of that state will be notified and the least amount of code will be run before updating the DOM surgically. React instead re-executes the code of entire component trees, compares the result with the current DOM and then applies changes. This is a lot more work and a lot slower. Over time techniques have been developed in React to mitigate this (Memoization, React Compiler, etc.), but it still does a lot more work than it needs to, and these techniques are often not needed in other frameworks because they do a lot less work by default.

The js-framework-benchmark [1] publishes benchmarks testing hundreds of frameworks for every Chrome release if you're interested in that.

[1]: https://krausest.github.io/js-framework-benchmark/2025/table...