As I understand it, it's more difficult than that... though I'm not a lawyer.

Let's say {some company} and Apple have a cross patent licensing for some set of patents.

Apple releases some softer under GPLv3. {Some company} sues someone else for a patent in bash. Since Apple licenses that patent and distributes bash, Apple is now obligated ("must act to shield") the distribution of bash that includes that patent.

    If you distribute a covered work knowingly relying on a patent license, you must act to shield downstream users against the possible patent infringement claims from which your license protects you.

That wording of "knowingly relying on a patient license" and "must act to shield downstream users" are things that lawyers don't want to touch with a 10 foot pole. Would it mean that Apple would be required to defend the company that its patent partner is suing? Not a spot that lawyers want to be in. Furthermore, if you distribute GPLv3 software, it may mean that doing the cross patent licensing is more perilous... again, not a situation that lawyers or large companies want to be in.

https://github.com/apple-oss-distributions/bash/tree/bash-13...

There's Apple's bash distribution. If this was the GPLv3 version of bash and apple distributed a version that {some company} decided was infringing, and {some company} sued you - "I got it from Apple. Apple Legal, help me."