I can only think of one other preposition that might make sense in the sentence you have provided and that preposition is the word, "for." Both "of" and "for" are commonly used in sentences like the one you have provided. But, if you would like a reason why "of" was used rather than "for," it is normally due to the author or speaker's decision. Since there is no rule as to which is correct, the author may use whichever he or she likes.
However, if you want to be more precise with your use of "for" or "of," there is a slight difference in interpreted meaning. "It was crude [for] him to say that," gives the impression that the thing he did or what he said was crude, but that he is not necessarily crude but only acted improperly in that instance. "It was crude [of] him to say that," makes it sound as though you are crediting the person's crude words to their character because "of him" gives the impression that you are associating the person's actions with who they are as a person. Native speakers are not likely to think this specifically about the differences and are most likely to use both words interchangeably. But, I thought I should mention that there is perhaps a small difference since that is what you asked. (Also, sorry for the long answer.)