In the evidence they found, they couldn't find sufficient intent that she intended to violate the law to suggest persecution to the DA. That's quite different than what you stated and what you posit the FBI stated. Basically the FBI wasn't a mind reader and there wasn't an email that said "hey we should do this to circumvent the foia"
> they couldn't find sufficient intent that she intended to violate the law
This is the problem. It's not their job to find intent but that a crime had been committed and she should have been prosecuted. There are literally THOUSANDS of examples where someone hadn't intended to commit a crime and were punished regardless of that citing the often quoted "ignorance of the law is no excuse".
Hillary knew the law. She should have known better being in her position but she chose to circumvent the rules (for a number of reasons) and as a result the law was broken.
Her escape from prosecution is nothing more than a blatant public travesty of justice.
Breaking the law requires intent or gross negligence, and the FBI said there was no evidence of either (gross negligence being a higher standard than "extreme carelessness").
That's actually fairly hard to prove, and it's not really the FBI's job to make that accusation. Both the Clintons are lawyers so they know what line to not cross apparently. I don't care for her and I don't care for trump either so this election is unfortunate.
