Not a historian, but a former photographer.

There was never a time for professional photographers when B&W wasn't used. As far as fine art photography goes, whether for gallery work or magazine shoots, there's never really been a time without black and white. It's always been part of the toolkit, for a few reasons.

The first is that a B&W lab was really easy and cheap to set up for someone who wanted to fool around. You could turn a windowless bathroom into a quick lab for pretty cheap. One of the nice things about B&W film and paper was that they made it so that it wasn't sensitive to red light, so you could work under red light and still see what you were doing. That's not the case with color media. It has to be able to pick up all the colors in a scene, so it's got to be sensitive to the whole spectrum and it has to be handled in pitch black, which makes it quite a bit harder to work with. The chemistry and paper for color were more finicky, complex and much more expensive too. I think it's safe to say that because of this, every film photographer ever learned the ropes in B&W before moving on to color. So it was a skill that all photographers would have had starting out.

More importantly though, B&W film allowed you to take a much sharper image. Color film requires 3 layers, a separate one for each of the primary colors, so it was 3 times as thick. With every layer that light has to pass through, the sharpness of the light gets fuzzed out and makes for a grainy looking image. And since you needed to expose 3 layers, you needed more actual light to hit the film too.

Black and white was only a single layer, so it could give you razor sharp images with less light entering the camera. This is no longer the case with digital photographs, where the same sensor is used whether you're shooting in color or B&W, but with old school film, you could really see a difference. A lot of fine art photographers would only ever shoot in B&W.