I think part of the difference might be the wider range and more smoother gear transitions you can put on just one bike nowadays. And with electronic shifting you don't have to suffer cadence hits because you didn't shift the front and back correctly to the next higher or lower ratio.

For grand tours it lets the same bike be used for both flats and mountains. You don't see bike changes for mountains like we did in the past. I don't do TT, so I can't say if that's part of it.

New gearing technology is probably causing a lot of rethinking.