A couple of years ago when I sat for jury duty, during one of my last call-ins as it was, we'd been in the pool room for a good hour or so precisely because of the statistics you cite. The bailiffs were getting a bit antsy and kept leaving the room, only to return a few minutes later to answer questions from a few impatient jurors. As it turned out, there were something on the order of about 7 trials on the docket scheduled for that day, and the first 3 or 4 had already ended with a plea bargain by that point rather late in the morning. We were told they would usually schedule between 7 to 10 trials on average because most of the defendants would usually agree to a deal. They assured us we would be going to juror selection "soon" and went about their business.

The unusual thing was that the remaining trials also ended in a deal, and after staying for ~2+ hours, we were free to go. Out of my 3 months, I only ever sat on one trial but we did get called in quite a few times. I certainly didn't expect to be turned away because none of the scheduled trials actually went to trial.

As an aside, I had an opportunity at the end of my term to speak with one of the prosecutors (I was leaving my last session at the end of my term and ran into him in the parking lot as he was getting lunch) who expressed frustration with the drug laws for wasting taxpayer money and jurors' time. Very interesting discussion.