Why "of all" is used not "all of"?
The phrase "of all' is used in phrases to express surprise, disapproval, anger, etc about a person, place or situation. It is not the same as "all of" which simply means the entire amount of something. Ex: Who should I meet in New York but Max of all people! Ex: Of all the people in New York, who should I run into but Max! Ex: Of all the luck—I just broke a nail! Ex: And why did you choose Iceland for a holiday, of all places?