Also, how can he possibly answer any questions without making things worse.
For all significant questions his answer would either expose a complete disregard for ethics and privacy, or be "No comment". Either just makes it worse for him.
Showing up to explain yourself only helps if you're innocent.
For the guilty it's better sending a flunky with cue cards that read: "I don't know", "I wasn't there", and "I don't have that information available right now".
Yeah I agree, there's no way he could come out looking good.
On a side note I'm very happy with the way this has been handled so far by the British media and the government. The lengths that Channel 4 went to unearthing this story is really admirable and there has been such a fast response to it. Just seems like it's becoming increasingly difficult to feel optimistic about anything tech/internet related these days and it's been a nice change.
Facebook have form for sending flunkies to answer questions they don't know the answers to; therefore stalling the judicial process. If Zuckerberg had to appear he couldn't fall back on this.
Because having Zuckerberg there himself looks bad, and they're already losing a fuck ton of money over this.