I'm willing to bet he can't answer that any more than I can say why the systems I support go down. Privilaged information, half the time it comes back up without explination of what happened from up top.
I don't work for the company I mentioned above however you are correct, they do not always volunteer as to why their network went down...bad publicity.
Sometimes we get lucky though and their rep will tell us it was caused by a number of reasons such as a software upgrade gone south, a critical switch bit the dust, server(s) meltdown, DNS problems and many more reasons.