I've read and redread what you've posted.
Despite what you've posted (have I mentioned that I've read it?) I'm struggling to reconcile the skills being easy to learn with the fact that why goalkeepers tend to improve so much later in their careers. I would have taken that as a sign that the skills were harder to learn rather than easier (which is what you've posted - I know, as I've read what you posted).
I think the discrepancy that you're so angry about might be because you think of the skills required as being (basically) the physical ones of catching, throwing and kicking. Perhaps we see the skills as running a little more deep than that, for example, positioning, motivation of defence, speed of decision making, etc, etc.
You even betray your thinking by the wording of your final question which specifies physical skills. I contend that the physical skills are not what makes the goalkeeper.
Vin