I agree with the additional points made that part of the reason for black is because of its association with carbon fiber. If you paint those cheap to midrange components black, they look like the might be carbon. Also, it's just fashion. However, I would argue that the component and bike companies play a big role in driving what becomes fashionable.

I'll stick by my initial explanation that cost was the original driving factor. Shimano and others started experimenting with painted components in the late 80s (roughly) primarily to save polishing costs. They were typically gray though, not black.

Going back another decade or two, there was some black going on in the 70s. We think now everything was all silver but it wasn't. Black was somewhat rare, and definitely associated with high end. The mid level was still pretty much all silver. In the high end, some of Campagnolo's competitors had some black components to make their gruppos look a little more trick. I'm talking about Dura Ace, Zeus, Galli, (some) Stronglight, et al. Certainly black rims when first available were seen as just insanely exotic. Martano blacks, Mavic SSC and even GP4's were introduced in the late 70s, but were highly unusual. The first black rims I saw - not counting old roadsters - were the Martano blacks that were originally on my '78 Masi. This is why a few years later in the 80s, bike companies started spec'ing black rims for everything. It made bikes seem to be higher end than they were. And here we are.