Meta has React, RocksDB and pytorch, and a few other "niche" frameworks and tools. "Half of the internet [...] run[ning] on open source code and infrastructure that Meta built and maintains" is a big, big exaggeration. Also maintainance is done by the OSS community for big parts, and I'm really curious what open source infrastructure Meta is running.

I'm not saying Meta has no relevance in OSS, but I can hardly think of an open source org that does open source purely for its own benefit. React helps them shape the web in the way Meta wants it, their ML stuff is important for their own internal needs (ads, BI, and the whole social networking, etc.), their AR/VR/XR contributions are for the Quest, and KI/LLM since they need it themselves instead of relying/partnering with OpenAI. Meta (the company) absolutely does not stand by the principles of open source, no matter how much you want to sugarcoat it.