Open source is just a family of licenses. Nobody is "open source". There is no single entity nor there is a single unified community with shared values behind it. There are just many many projects/applications developped by entitites completely different in nature from the single hobbyist developer to the giant hyperscalers you mention with pretty much everything inbetween with vastly different goals, sizes, profesionalism, funding. And there are many different reasons to choose an open source license, some do it to attract contributions, others for the freedom it offers to the users and developpers, some want to force the license to stay the same, others do not mind if forks are proprietary, some companies will just do that for the optics/marketing and have more featureful version of their product sold under a proprietary license, etc, etc. You can't just put them all under a single "open source" banner and pretend "they" (whoever they are) need to fight against anyone else.