Why don't Cap and El Santo get Adaptational Nationality like Spider-Man? Because their concepts are tied too heavily to their countries of origin. It would be harder to explain why a Turkish detective was wearing an outfit based on the American flag or dressed like what's obviously a Mexican wrestler.
Word of God is also that the featured superheroes were favorites from his childhood, and that he chose Spider-Man because he wanted an especially powerful foe to oppose Captain America and El Santo.
