I think you misunderestimate the talents of many brilliant individuals available. I've worked on some cases that lawyers had trouble understanding but I didn't.
No. I don't believe lawyers have any monopoly on intellectual capacity or ability to communicate. However, the legal issues presented in some of these cases are complex, even for people who have studied the subject to the point of being expert in it. It is one thing to understand a concept, but it can be quite another thing to understand its importance in the relevant universe of concepts. A non-lawyer, no matter how smart and gifted, would have a lot of trouble doing that in many of the cases that come before the court.