Judges have minimal training in the procedures of the court. Some are attorneys which gives them more familiarity with law and process, but as far as I know that’s not a requirement.
The jury selection process has nothing to do with qualifications of jurors. The prosecutors are primarily trying to eliminate people they think will be sympathetic and the defense is primarily looking to eliminate people they think might biased against their client.
The lack of legal training is exactly the issue at hand.
Juror selection isn’t about qualifications. However, it does give both sides an opportunity to eliminate vested or deeply unqualified interests that may be biased against them. With a judge you have no such option.
Except for appeal. If a judge gets overturned enough on appeal, they can rightly be said to be unreliable. Which means, if they're elected to the position, their opponent can site how many times they got overturned as a legitimate reason to think they're bad at their job.
All of this functions well... unless the electorate is uneducated or misled, and apathetic. That's the real problem in this case. People are winning popularity contests, because the only thing middle and high school taught most of the electorate was that you should be popular.
It isn't true everywhere. Reputation and reputation systems can and do function well. But they require a functional press, and an interested public.
Jury trials also have jury selection processes that allow lawyers from both sides to eliminate any poorly qualified jurors.