Just generally speaking, code that does orchestration and testing in general is often easier under a dynamic scripted language over something that is built and compiled, even if it winds up as a custom DSL. I think Python is one of the better options here for the broader community support, and tooling.

Aside: I tend to reach for node/js often for similar reasons (despite detractors) mostly because I'm more comfortable with it over Python or Ruby, but also because it's already integrated to most of the build/test environments I'm working on anyway.