This was a strange group for me too. I don't like Fellini, but I Rated him a 4. The other 3 are above a 7. I tried to figure out why these filmmakers have detractors. My initial thought with Zinnemann was A Man For All Seasons, but then I remembered High Noon, which Western purists tend to dump on.
When I saw the 10 for Chaplin, I just assumed it was Oldkid. I rated him 7.4 myself, mainly because I've seen too much of him and I think he has a number of 2nd tier works - King of New York - that get more attention than they deserve. He has a number of gems, but is a director like Fellini where people see his name and automatically reward it with Greatness.
My initial thought on low Ratings for Leo McCarey was his connection to The Marx Bros. (though he only did one of them). I know some people don't like Make Way For Tomorrow, but it should be balanced by those who love it. Going My Way, considered one of the least deserving Best Picture winners, became my best theory.
FYI, the person who Rated Chaplin 2 also rated McCarey a 2.