I don't think this is a particularly interesting take. Google's utility c++ library isn't that different from eg underscore.js (or lodash)

Google uses some boost code and plenty of other external libraries (I can't speak to Facebook but imagine it's similar) - I think the point is just that Facebook and Google have an enormous amount of c++ code and have thus created libraries (some of which are fundamental enough or self-contained enough to open source)

This is just what happens when a bunch of engineers are all working in the same language - the utility libraries become large enough, robust enough and useful enough to open source

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As an aside, I think the similarities between folly and absl say something more meaningful about the state of c++