Black Nikon F's are much less common than chrome and people ("collectors") pay a premium for them. Even more so for the Nikon rangefinders. By contrast, black Nikon F2's don't seem that uncommon, but maybe they are still a bit in demand. The black ones tend to get pretty brassed up at the corners so maybe there is an extra demand for unbrassed examples.
In the 1980s or so, the midrange Nikons (FE, FM, FE2, FM2, FA, even the FG) were all available in both black and chrome, and IIRC the black bodies usually cost some small amount more, about $10.