Simply desaturating a photograph doesn’t really represent a true black & white film photo. The film has more impact, more puch and more life. A digital photo converted to black & white just doesn’t cut it, it doesn’t look real.
Although it’s impossible to represent digitally what the chemicals and the paper do to a black and white image (not to mention the film), we can get fairly close to something like a TRI-X 400 film once we understand what’s happening with the film.