That's like asking "why would you use Swing when you can use Graphics2D". Sometimes you want something higher level. The DOM is great and very powerful, but when you're building a highly interactive web app you don't want to be manually mutating the DOM every time state changes.

I am a core maintainer of Astro, which is largely based around the idea that you don't need to always reach for something like React and can mostly use the web platform. However even I will use something like React (or Solid or Svelte or Vue etc) if I need interactivity that goes beyond attaching some event listeners. I don't agree with all of its design decisions, but I can still see its value.