There’s a difference between the single engine clear weather licenses most anybody can get if they’re just willing to spend the money and the time and the multi-engine instrumented rated license, that’s hard to get because those tasks are hard to do, and that’s what the passenger plane pilots have to be.
Do you believe that only a few thousand people in the United States have the ability to learn how to pass the multi-engine instrumental rating tests? Or is it more likely that most people simply never get the chance, or simply have no interest in, doing so?
What is so HARD about it? Does it require a PHD? Would a person have to have an IQ of over 150?