How would a successful antitrust verdict against Apple further the NSA's implicit dogma of "insecure by default"? Especially if it winds up breaking up Apple into many pieces. It's far easier for a centralized tech industry to bend the knee to the NSA than a distributed one.
easier but you get less data. There's thousands of small knees to get to bend to. More points of failures for public outings Centralizing it to one company makes everyone's lives easieer.
Furthermore the NSA/FBI/CIA want all their spying behavior to be secret. If you have to bend a lot of small knees then someone's going to fib before they get the data they want. And moving off a small company that's bent the knee is way easier than moving off FAANG, which can keep secrets[0] and has your balls locked in a vise.
[0] Because, among other things, the whole "Surprise and Delight" doctrine demands internal controls and secret-keeping discipline not that far off from an actual intelligence agency
Forcing Apple to hand over data to a third party for commercial reasons (not needing a warrant) is much simpler than whatever scenario you have worked out.
Apple looked at the pen register cases and realized the best position to be in as a third party is to not possess usable data.
The US case from my point of view is trying to fore Apple to share user data with third parties.