Because of the manner and the timing of the whistleblowing. The courts usually hear these cases fairly quickly, because of the risk of leaks. There was no real need to identify Green now, except to embarrass him (but he seems fairly impervious to public opinion) and to put Hain in the spotlight.

If the court were to decide in favour of the Telegraph then Green's identity would have emerged anyway, and quite soon. If not, and the court had made the injunction permanent, then Hain might arguably have had more justification for naming him under parliamentary privilege, given the other controversies surrounding him and the pressure to remove his knighthood. It could then be argued that the public interest overrides a private contract, but at least the court would have had a chance to decide.

Why does this matter? The rule of law is the only protection the rest of us have against the rich and powerful. Admittedly it is imperfect, and lawyers are expensive so the rich hold an advantage, but it's all we've got. I happen to think that's more important than whether Green is further embarrassed now or in a few days' time.