The other ingredient here is that the Elite who decide who the Democrat candidate will be may be using the FBI probe as a cover for their actual decision.
She is tumbling in the polls and the key states and internals are even worse. I’m sure the Elite do their own polling. If they want to replace her with Biden or Sanders they will have to do it soon. The FBI probe will be the excuse. Lynch taking her stance as she did makes it look like a non-political decision, and distances Biden, Sanders, and Obama from the process.