Obama wasn’t going to be exposed (indicted?) because of Hillary Clinton. As such it was vital that HILLARY not be indicted which might have started toppling other legal dominos.
(From The National Review)
If Clinton had been charged, Obama’s culpable involvement would have been patent. In any prosecution of Clinton, the Clinton–Obama emails would have been in the spotlight. For the prosecution, they would be more proof of willful (or, if you prefer, grossly negligent) mishandling of intelligence. More significantly, for Clinton’s defense, they would show that Obama was complicit in Clinton’s conduct yet faced no criminal charges. That is why such an indictment of Hillary Clinton was never going to happen. The latest jaw-dropping disclosures of text messages between FBI agent Peter Strzok and his paramour, FBI lawyer Lisa Page, illustrate this point.