It is a way to signal to other developers that your code changed, which is better than not saying anything.

But it seems to make library developers more comfortable with making breaking changes. It's like they're thinking 'well it's documented, they can just change their code when they update and get errors in their type checker/linter.' When I think they should be thinking, 'I wonder what I could do to make this update as silent and easy as possible.'

Of course, we all have different goals, and I'm grateful to have access to so many quality libraries for free. It's just annoying to have to spend time making changes to accommodate the aesthetic value of someone else's code.

But it also makes it easier for library developers to identify that a change is breaking. Without static types you can easily make a change you think is fine, but it ends up breaking user code because they depended on something you didn't expect. Granted, static typing doesn't completely solve that problem, there can still be changes in behavior that break things, but it is a useful tool in identifying certain classes of breaking changes.

I think the only time I’ve ever seen this is in a JS library, where each major version bump is practically a different library altogether because it’s a complete rewrite, and these days is a wrapper around some Rust thing.

Not even JS alone. I blame the enforcement of semantic versioning, as if a version of code simply had to be a sequence of meaningful numbers.