As said above, in the seventies silver exemplified quality. In the eighties it seemed to me that when it came to uniformity, silver was more difficult to keep uniform. In a rack, mixed silver looked tacky. Black was easier in that regard.
I think that home theater setups (no glare on black) in the eighties as well as a trend toward American manufacturing influenced the change. The seventies were completely influenced by the Japanese market and their demand for silver faceplates. The Japanese still demand silver. There were many pieces of gear they made where silver was only available in Japan. I agree with the Japanese. I want my gear to look as good as it sounds. I don't mind black components. They should be aesthetically pleasing however.