I think the move back to side pulls probably was facilitated by the move to tighter clearances allowing for the short reach brakes so that the lack of efficiency wasn't so drastic. The the reduced weight possible did make them preferable. Plus the lack of a need for a cable stop on the headset and seat post clamp...

The dual pivot design obviously helped braking efficiency too.

The latest Campagnolo brakes have gone back to single pivot for the rear brake where efficiency isn't as critical to save a few grams.