Node also introduced a stable extension API that people could build native code against relatively early in its history compared to Python. That and the general velocity of the V8 interpreter and its complex API kept developers from reaching in like they did with Python, or leaving tons of libraries in the ecosystem that are too critical to drop.
Yeah, I think it's mostly about complexity: CPython's APIs also change quite a bit, but they're pretty simple (in the "simple enough to hang yourself with" sense).
