There are a lot of comments along the lines of "why are the fines so low" or "why is nobody doing jail time?" And the answer to both those questions is: stiffer punishment would require stronger proof. Cartel activity, like much white collar crime in general, is extremely difficult to prosecute, because the difference between totally legal conduct and illegal conduct comes down to what people are thinking. Instead of…
Er, why shouldn't he be? I can think of three main likely arguments why he shouldn't:
i) what he did breached civil but not criminal law: if so then obviously he shouldn't be in jail. I don't know whether that's the case though. I also don't know if he is personally liable for civil damages, and if so why he hasn't been chased for those. (And that's not going into the question of whether his actions should have been made criminal offences by law, and why they haven't been.)
ii) the higher standard of evidence in criminal prosecutions, the first issue you raised. This is of course a real issue in criminal cases, but—speaking as a non-lawyer, non-expert who hasn't been following the story very closely—the evidence on this matter doesn't look at all lacking to me. AFAICS, if Eric Schmidt had been discussing a murder rather than salary collusion in the communications discussed by http://www.businessinsider.com/apple-google-recruitment-emai... no-one would be likely to suggest that the evidence was too weak for a criminal prosecution.
iii) Eric Schmidt is a nice person like us, and jail isn't really for nice people like us. I hope the egregiousness and total unacceptability of this argument is clear to everyone without any need for explanation.
So, yes, why shouldn't Eric Schmidt be in jail?
As to the financial sector, while it is obviously difficult to prosecute many financial crimes, I am not convinced that this is the primary explanation for the shortage of convictions lately. I am reasonably convinced by the argument http://neweconomicperspectives.org/2014/10/liars-loans-aint-... that similarly complex cases were successfully prosecuted in the S&L scandal in the '80s, and that the primary difference between then and now is lack of resources and political will.