Maybe three decades ago, but I recall that when I was racing mountain bikes, narrow rims were the fashion. There was some debate about it, but most of the racers I knew seemed to opt for 17s rather than 21s. As a result I still have two sets of wheels built up back then with Araya RM17s and Deore XT hubs and have always run rires wider than 2". I'd don't remember what the rationale was behind the choice but it was a popular one enough one at the time, that people actually switched to narrower rims in some cases. FWIW, I still sometimes ride the bike they were built for and enjoy it. I still would use it for a mixed surface tour.