I am not a huge fan of NIH but more often than not it is simply easier in the long run to roll something in house that does the job. Although the debt that piles up tends to dwarf the original choice it is often still a better idea due to having employee churn. Its much easier to keep it within the standards of normal coding conventions.

I don't work at FB but near the bottom in the comments you can see that they build on existing C++ libraries that have been tried/tested. We do the [same thing][1] with smaller services simply because its easier in the SDLC process to move libraries that are already in-house.

[1]: https://github.com/bloomberg/bde/tree/master/groups/bsl