I’m a bit cynical, so take this as thou wilt.
IMO lawyers are often more concerned with winning a case than discovering the truth. In a criminal case the accused is paying his lawyer to keep him out of jail. In a civil case the plaintiff’s attourney often gets a cut of the award. So there’s incentive to win.
For example, suppose an airplane crashes. Even if it is fairly evident that the pilot did something stupid (“Hey, let’s see if there really are violent updrafts and downdrafts in that massive thunderhead!”) the family may sue the aircraft manufacturer for not making an aircraft that would survive conditions that a reasonable person would say are unsurvivable. They may also sue the engine manufacturer for making an engine that was not powerful enough to get their loved ones out of harms way quickly, or that they alledge stopped at an inopportune moment (Gee, could the pilot have forgotten to refuel?) Then they may sue the FBO that rented the airplane to the pilot, on the grounds that they failed to provide proper maintenance or rented it to him when they “knew” conditions were bad. The guy’s flight instructor may be sued on the grounds that the instruction (even though the guy passed an FAA checkride) was lacking.
Now there are a couple of things to consider. Pilots can be hard on other pilots. They might hear the evidence and say, “What an idiot! I would never taken off in weather like that! Or if I did, I wouldn’t have gone anywhere near a thunderstorm!” The bereved family’s attorney is not going to want anyone who knows anything about aircraft on the jury if he can help it. Another thing is that the “general public” tend to fear “little airplanes”. People who don’t know about aircraft tend to think they are dangerous. Since the attorney’s goal is to win a fat settlement for his clients (and a 1/3 portion for himself) it behooves him to “stack the deck” by excluding as many pilots (and we all think we’re “experts” 
) from the panel. On the other hand, the defending attourney would want the opposite.
In the case of DNA evidence, the accused defence would not want someone in the jury room to point out that the prosecutor made a stronger case because, “this is what they taught us about DNA, and by the way I’m at the head of my class”.
So IMO the reason they want to exclude “experts” is that the “experts” may ruin their case for them. Another reason is that an “expert” mightn’t know as much as he thinks he does. This could skew the case the other way. I think that they play it safe by excluding unknown quantities from the jury.
What the lawyers want to do is persuade the jury of the rightness of their case. Ignorant people are often more easy to sway than more intelligent people. Intelligent people can weigh facts, whereas people who aren’t quite as swift can often be manipulated by emotion.
All of that said, there are intelligent people who do get on juries. But having been called to service several times my own experience is that I would not want to spend time with most of the people in the jury pool.
BTW: I’ve been called again for next month. Sheesh, a woman I work with – who is about 25% older than I am – has never been called!
YMMV.