1. most devs know JS (so it's easier to hire & onboard new devs)
2. while everyone claims node's dependencies are hell, I love the choice available (although over time, it's tiring).
3. The community is generally awesome (helps during meetings, online etc.)
4. Developer Exp: With TS, Tslint etc, devx is not too bad IMO (and there's no dearth of opinionated articles around on the correct way to do things)
5. Finally - we can quickly churn out prototypes for features to production (but I guess that's more experience than the tools?).
6. In general, we'd be using JS on the frontend anyway (React), so it just made sense to use one language everywhere.
7. In general, most tools have JS SDKs and JS language support is always around (an exception I found was Tensorflow) - as an example, AWS Lambda supports Java, Python and JS.