Larzuk appeared to be on the verge of discovering gun powder, but shortly thereafter he was killed as the mountain exploded on his head. Thus the secrets of gunpowder are lost forever and have no chance of being rediscovered. Because we say so, and thatâ€™s how fiction works.
Yeah a little bit of exaggeration but you got the general sentiment right.
Guns are decidedly scientific, and the Diablo world is decidedly magic (with a lot of impaling people on pikes). Not that guns and magic canâ€™t mix, but when they do it becomes something entirely different. So I donâ€™t think itâ€™s an issue of guns not being fun or just not working, itâ€™s nothing like that. Itâ€™s simply a setting and tone issue, and guns would very certainly change it.