It could indicate that judges are overeager to convict, or it could indicate that prosecutors are unwilling to try someone they aren't really damn sure of. Or a combination of the two, or probably a bunch of other reasons.
Additionally, many prosecutors, police and people in the criminal justice system believe that, even if the defendant is ambiguously guilty of the crime they are on trail for currently, they are certainly guilty of other crimes they are not currently on trial for. Thus shading information to get a conviction in an ambiguous case is sometimes viewed as a public service. Interestingly this part of problem is not the result of malice or even ambitious DAs.
Judges don't convict, juries do.
Just thought I'd clear that up.
http://litigation.findlaw.com/going-to-court/judge-versus-ju...
>Plea bargaining in the United States is very common; the vast majority of criminal cases in the United States are settled by plea bargain rather than by a jury trial.[1][2] They have also been increasing in frequency—they rose from 84% of federal cases in 1984 to 94% by 2001.[3]
Also note judges don't have to accept plea bargains.
So each party in a case decides whether or not to have a jury based on these points.
To a limited extent, attorneys can ask to change judges. Judges are embarrassed when they are "papered" this way so this provides pressure not too be absurdly biased.
And finally, there are a few differences in laws and huge differences in both judges and jury around the US both in opinions and education level. Dare I say this is why patent cases all end up in East Texas.
I noticed this about 20 years ago. Campaign ads for judges usually focused on how "tough on crime" they were as opposed to how "fair and trustworthy" they were.
I lost what little respect I had for the legal system when I watched a prosecutor argue that two convicted men should remain in prison and one should remain on death row despite newly discovered exculpatory DNA evidence and new evidence of police and jury misconduct because "The system" needed finality.
If it came to that, a trial by judge versus a trial by jury might have a better outcome than relying on a group of laymen who just want to go home to decide your fate.