Their friendship is absolutely critical to the film. The film communicates their relationship pretty well, so how they became friends, x number of years before the events of Monsters Inc. is not necessarily a story worth telling. I doubt many people watched the movie and said "Okay, I followed that for the most part, but how did these guys even become friends?" People have friends. That's pretty easy to accept.Quoting Fezzik (view post)
It might still make a good movie, I guess. But the premise is the stuff of fanfiction.