> Copybara doesn't have a release process yet, so you need to compile from HEAD.

Looks like there's an Arch Linux build maintained by... somebody, but if you're not on Arch then you're going to be building Copybara with Bazel. That this works for them suggests to me that their community has a significant amount of overlap with the Bazel community, so it's not good evidence of Starlark being used outside of the Bazel world.

Lots of projects developed at Google use Starlark. Copybara is one of them. That's where the connection comes from.

Many other companies are also adopting Starlark for their own needs. For example, Meta has invested a lot in Starlark and published their implementation (https://developers.facebook.com/blog/post/2021/04/08/rust-st...), although they don't use Bazel at all.

Starlark was first created for Bazel. The organic user growth comes from people who have seen and used the language, so often Bazel users. But it doesn't have to be.