It doesn't, parent is suggesting everyone benefits when cloud providers use their accumulated wealth to hire people to work on their OSS investments as some kind of justification for the consolidation of wealth from OSS happening around cloud monopolies.

It doesn't benefit everyone, it benefits anyone using their proprietary and OSS products and cloud services. It definitely doesn't benefit existing OSS projects who are seeing their innovations replicated by full-time resources or OSS developers working on competing projects.