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?
Yes. What’s so hard about it is the level of complication, multi-engine planes are hideously complicated devises that the pilot has an extreme high level of control over. Imagine if with just the flick of some switches you could change every single aspect of how your cars wheels interacted with the road, individually, on the fly, and you HAD to do that in order to drive. Then add being able to change how body of the car was shaped, altering your aerodynamic signature to the point where you can actually steer it... in 3 dimensions. That’s life in a multi-engine plane. Then add the ability to do all without being able to look out the windows, that’s instrument rated.