> wouldn't it make more sense that the environments supply what's meaningful on top of a very light base

I certainly don't think so. JavaScript is a language that works in more places now; commonized libraries would be a huge benefit. As an example you wouldn't use Python with different io libraries depending on the operating system it's running on and yet this is what node is evolving into.

> Like window.document.querySelectorAll in browser and require("fs") in node.js?

querySelector / querySelectorAll are specific to a browser platform but a way to conduct io could be pretty universal, in my opinion.