1. fast development (both Python and node)
2. boring platform where it's usually OK to leave smth unupgraded for >5 yrs (Python wins here hands down)
3. cheap devs (good Node.js devs have a lot of option to "jump around" between front and back and frameworks so higher room for leverage ...with Python you can hire cheapest newly grads since it's now taught in most unis)
...on top of this:
- performance in terms of "requests served per CPU power" does NOT matter for most apps (and when it does caching saves most situations) - and if it does, modern Python can deliver now (async is mature)
- using same stack as ML and datasci comes as a bonus - you can have backend-full-stack-devs jumping between data pipelines, APIs/web, ML models, data analysis code etc. who can stay separate from frontend-full-stack-devs doing web frontends + mobile hybrid etc.
It would be great if we could also standardize on a static high performance language common to all (eg. usable for special-performance-sensitive-code either standalone services or Python-modules or node-modules) ...this area's a mess, too much overlap, duplicated work, and too hard for devs to jump from one ecosystem to another (Rust and C++ as lib/extension langs... Java/Kotlin or Go or C#/F# for standalone services... now Swift an option too...).