TBH, I worry a lot more about this kind of thing in the case of Google, where they can afford to give away things that other companies would have made an entire

TBH, I worry a lot more about this kind of thing in the case of Google, where they can afford to give away things that other companies would have made an entire business out of, which devalues those markets, then they lose interest and sunset it all— and only in a few cases (like Wave) does any of it end up open source. But FB isn't really competing with other companies here. They're giving away frameworks, libraries, tools— this is building block stuff, and the fact that it's perhaps particularly optimized for FB's workloads is just their privilege, having been the ones to fund it.