Ajit Pai is a public figure. All of his personal information is already within the public record, there was no need to hack anything to find it.
Really, the purpose of a hack like this isn't so much to get that petty information, but to send a message that other information could also possibly be obtained. Today it's just an address and some names. But tomorrow it could be a list of major donors or evidence of some misconduct, something much more potentially embarrassing, and the place of actions like this in hacktivism is to send a message that "we're watching you, you can't hide anything from us".
As for the harassment angle, I have no sympathy at all for people who align themselves with the alt-right and then complain about harassment.