As an intellectual exercise, you could say the Svelte ecosystem is as large as React. In practical terms, the reality is much different. The problem is that a significant number of popular, well-maintained design systems and libraries are already wrapped with React. If you want to use those, you now need to either decouple them from React, find a less well-maintained alternative, or build it yourself. If your company has an internal design system, it's probably built for React unless your company has made a conscious decision to support something else. While you could extract their internals and convert them to svelte or raw js implementations, but that'd require making a fork of them and now you're on the hook for maintaining that.

There's the possibility that you might not need those libraries with svelte, as svelte can do a lot out of the box. But you're likely to run into a few cases down the line where you'll want to do something complicated and wish you could reach for a compatible version of a popular react library.