Because some of it is.
I will explain, first of all, Google saves everything, they have and are building more superstructures just full os storage media to accomplish this. that said if a person from anywhere sends Hillary an e-mail thru a Google account, Google still has it. When you can access your g-mail account from anywhere, you are not accessing your computer, you are accessing a Google computer hard drive somewhere. Hillary had her own network, but not all of the dimwitts communicating national security information to her server had their own server. Thus if they used a Google server, that server still has that e-mail somewhere. It's real, and the U.S. government has no access to this, nor can it prevent this info from falling into enemy hands.
Now-classified Clinton emails sitting on Google servers
This is the dumbest move by a U.S. politician ever, way bigger than Watergate, and it involves tens of thousands of people in thousands of places, all around the World.