A big thing is support for island architecture [0].

Essentially it only pulls in the JavaScript it needs to make an element interactive; you can mix frameworks on the same page, and it's very fast.

https://docs.astro.build/en/concepts/islands/

I chose Astro for my personal website because these things all aligned with my thinking in this space and desires for a tool: https://docs.astro.build/en/concepts/why-astro/

Astro also does SSR. I'd say that Astro is special in the ecosystem because (1) they went all-in on MPA and (2) they support many component frameworks.

Astro is really good at rendering JS on the server out of the box, while letting you quickly fall back to dynamic content as needed.