Skimming chalk's releases page, I did find some quick confirmation of what I expected: recent releases, at least breaking ones, are to do with keeping up with ecosystem changes:

https://github.com/chalk/chalk/releases

5.0: moving to ESM

4.0: dropping support for Node <10

3.0: indeed some substantive API and functionality changes

I got to 2.0 which added truecolor support. I was amused to note also that 3.0 and 2.0 come with splashy banner images in their GitHub releases

This is a pattern I've seen often with "connector" packages, e.g. "glue library X into framework Y". They get like 10 major versions just because they have to keep updating major versions of X and Y they are compatible with, or do some other ecosystem maintenance.