https://en.wikipedia.org/wiki/Tortious_interference
> Tortious interference, also known as intentional interference with contractual relations, in the common law of torts, occurs when one person intentionally damages someone else's contractual or business relationships with a third party, causing economic harm.
In this case, people who use GCP have customers and other contractual relationships. Google's termination of service interfered with that. Google also doing this as a matter of standard business practice indicates that they are aware that their action will interfere with people's contractual obligations (well common sense should tell them that anyways).
You can't force someone to sign a contract with you that says "if I interfere with your future contracts with arbitrary third parties on purpose, you can't sue me". The deliberate part is crucial from what I understand. If their decision making couldn't have accounted for the interference, and the interference wasn't calculated as an acceptable risk, there is no issue. But the plaintiffs can claim that repeated social media posts and acknowledgements of said interference by Google over the years means it's enough grounds for a suit. and a suit will mean discovery, google will have go hand over internal documents, depose employees,etc...
In the end, this might be more costly to companies like Google than just giving customers a grace period to move elsewhere before termination.
Obligatory: IANAL, I'm just a guy using big words I barely understand.