For one, I just don't think we are very rational. And I am including myself in that.
And, like this case, the personalities reflect exactly what happens when you gether a dozen individuals. One or two are loud-mouth bravados, a few don't speak, and some are just apathetic. It's nice to think that I would be that disagreeable person who would stand my ground, but I am not sure.
Sometimes I wonder what we would do if the courts were designed today. I am pretty sure we would not come up with a system where we gather 12 random people. I don't know what we would decide on, but almost certainly not this. But like many things, it varies on because no one has an obviously better way.