I can't tell if this is a good faith question, but in the interests of good discussion, there are many ways they can do this. Technical solutions include blocking the user agent, blocking request patterns, client-side feature detection, client-side attestation, but importantly they are not limited to technical solutions, there are also things like cease and desist letters, breaches of contracts, pressure on the software distributors, lawsuits.

This is no judgement of whether these are the steps they might take, or whether they would be right in doing so, I want to remain neutral on this. But I would point again to the many instances of things like this happening in the past.

Like most things.. it is a cat and mouse game dependent on how heavily they believe their revenue could be impacted. I am not sure why you think either of those corporates would have a problem of banning individual users, who are only suspected based on the app signature..