I think it's more of a strategic difference. Google seems like their long term planning involves thinking about open source less than Meta's. They're more wait-and-see about it.

React must've been destined to be open source from the get go: gotta create a mountain of js to hide in so the users can't strip out the malicious parts. Kubernetes on the other hand could've been internal forever and still would've made sense. It just happened to later make sense to open source it (it feels lopsided to me, like they kept certain parts secret. It wouldn't feel that way if they had planned it as OSS from the get go).