It's a free-rider problem - if large cloud companies fork every successful open source infrastructure project, don't contribute back, and pull away a significant chunk of users, then there's a lot less incentive for other companies to invest in future open source development, because they'll have fewer users and get fewer code contributions.

Potentially that shifts things from a good equilibrium where everyone reaps the benefit of many people contributing to the same projects, to a bad equilibrium where every major cloud player develops closed-source products separately.

I don't think it affects all open-source projects, particularly not small ones or ones where some is scratching their own it. But it's hard to build certain types of complex production-quality infrastructure without full-time employed developers working on it.