Remember, recipients of GPL code (companies in this case) are not affected by the terms of the GPL until they redistribute the code themselves, until then they can add proprietary code all they want, run it on servers and never release a thing. They are completely free to USE the code however they wish.
So in this example, no cloud company has to release changes to their running linux kernel because it was never distributed to end users, or at all.
Same for all other GPL code running on servers, users of the service, loading web pages and using APIs, are not recipients of the code under the GPL, so they have no rights under the license.
If some company decides their changes to the kernel, or nginx, or apache, or php can be released because it won't destroy their business, they frequently do so. Otherwise you'll never hear about it and changes silently remain secret.
So in this example, no cloud company has to release changes to their running linux kernel because it was never distributed to end users, or at all.
Same for all other GPL code running on servers, users of the service, loading web pages and using APIs, are not recipients of the code under the GPL, so they have no rights under the license.
If some company decides their changes to the kernel, or nginx, or apache, or php can be released because it won't destroy their business, they frequently do so. Otherwise you'll never hear about it and changes silently remain secret.