Widescreen and color both came to cinema in a big way around the same time in the 50’s so the number of films shot in widescreen and black and white is comparatively small. However there are an unusually large proportion of good films among them: The Longest Day, The Apartment, Yojimbo/Sanjuro, The Hustler just to name a few.
This is a nice blog postwhich looks at some black and white widescreen films and examines whey they look so good. As it says some of it has to with the anamorphic widescreen format itself but I also suspect there was a selection effect at work. This was the time when color was quickly becoming the default and perhaps it required a quality director with a fair degree of clout to hold out for black and white: Kurosawa for example. Therefore the few of these films that were made tend to be of high quality.