This was an easy and popular choice to take. McKinnon was not a threat, and the US "World Police" stance has weakened a lot since the GWB days. Even better, it's an election year in the US in which an incumbent President has to motivate a disillusioned left wing; he really doesn't need the backlash following a potentially unpopular extradition.
The point had already been made: subjects of the Empire (which Western Europeans people are, de facto, especially if living in Britain) who dare attacking US military infrastructure, even in jest, will be hunted, and their lives made miserable. Whether they're actually going to be sent to Gitmo is irrelevant in practice: McKinnon's life is forever compromised on many, many levels.
So, in practice, Obama(/H.Clinton) doesn't give a rat's ass about McKinnon, and the Coalition has enough problems as it is, there's a good chance to score some cheap political capital, so why pass on it? Add to that the recent announcement about opting out of some EU laws, and you can see that May is positioning herself as friendly towards the right wing, classically "individualist" Tory faction which is currently threatening to "tea party" Cameron, and all without spending any money (which, in government, is always the best sort of action). I don't think there's anything "moral" in that; it's just another day in UK politics.
I find her insidious and duplicitous. When did we last have a Home Secretary who wasn't a careerist authoritarian?
Nevertheless I strongly suspect that today a life has been saved and hopefully from now on we can apply rationale to our extraditions.