Apple doesn’t have the keys to it. That’s one of the major points of iMessage. Your keys are generated on device only. Apple can’t give what they don’t have. With the newer keychain stuff they’ve also made iCloud end to end encrypted as well, using keys generated on device, if you use advanced data security.

And if they would, they wouldn’t have gone to court over it when it was literal terrorists, the San Bernardino shooters a decade ago. They couldn’t turn over the keys to their iMessages because they didn’t have them and they went to court after they refused to put a back door in for the US government.

There’s a LOT to hate about Apple, but privacy so far hasn’t really been one of them. They’re pretty transparent about privacy features and how data is handled.