I wouldn't be surprised if the connotation of being unlicensed had something to do with it, but growing up (and studying jazz with many accomplished musicians)

I wouldn't be surprised if the connotation of being unlicensed had something to do with it, but growing up (and studying jazz with many accomplished musicians) I always heard the etymology that it has always referred to faking one's way through - which is the supported etymology in the linked article, as well. Personally I believe that words typically have multiple concurrent etymologies which all have some validity, and that's probably the case here IMHO, so, again, I think you make a fair point. Since we're getting into technicalities, a "lead sheet" is not exactly synonymous with "fake book". A fakebook encapsulates a particular sort of standard repertoire, it is a curated assemblage of standards as much as it is sheet music. As such it's almost impossible for a fakebook of the most general sort to be fully licensed. (And when Hal Leonard came out with the legal Edition 6, many musicians rebelled and stuck to the pirated older editions because they covered the genres more comprehensively).