Bright Shiny Chrome is so 1950's....

The black may have been coming for a while, but it certainly became popular with the carbon fiber bikes and carbon fiber components.

Campagnolo, of course, has carbon fiber brake levers, carbon fiber cranks, and carbon fiber derailleurs in their top of the line components. Black just goes well with those.

And, for lower quality components. Plastic instead of carbon fiber... still black, and largely mimicking the carbon (and plastic generally doesn't mimic aluminum/chrome well). Then for aluminum cranks & etc... still black like the Record/Super Record.