As someone from the UK I am not at all surprised, there is no upside to him doing so. There is nothing he can say that will help, the committee will absolutely rip into him as their primary audience is the press and people of the UK, they don't really care about his answers to their questions. The problem is that the story isn't about FB making mistakes, or being hacked, or doing something they said they wouldn't. It…
If the vast majority of users are only working out what they have signed up for now, after using the service for years, then it would be hard to argue that Facebook's users have given informed consent to a contract, which is generally a legal requirement here for it to be said that you have agreed to something.