The one thing I like about Astro is the component island UI. With react you would need to re-render the entire UI on a UI change while in Astro you can signify which portions of your website are static and which dynamically should re-render upon data fetching or whatever.

It's just a faster way to build UI's that don't need the full complexity of a SPA and also don't need to come bundled with the entirety of react from what I've seen and used it for.