There was a time not so long ago when head shots — close-ups — were standardized in black & white. That’s the way they were done.
Possibly, it was because they were typically put in newspapers which were black & white — much less expensive to print for everyone.
Personally, I don’t think the quality of color in newsprint is worth looking at. They should stay with black & white.
I also think that black & white closeups are more interesting and dramatic than color.