In case you haven't heard, Hillary had a secret email server while she was secretary of state. It wasn't particularly secure, was allegedly wiped, then wasn't wiped, and we now know she used it to send gobs of classified information. The FBI's is pretty interested in it. They're also interested in allegations that she peddled influence at the State Department in exchange for donations to the Clinton Foundation.
When you're running for President, and you're the subject of a large - and growing - FBI investigation, you should expect to be asked about it. That is, unless you're a Clinton. If you're a Clinton, you think the media should lick your boots, ask the questions you've told them you'd like to answer, and thank you for gracing them with you presence.