The same question might have been asked when they went from single speed to two-speed with a wheel flop, to derailleurs. They went up slower before, faster after, and didn't destroy themselves as much on the climbs.
At the '87 Pan Am games in Indiana, everyone assumed the road race course would be flat because that's Indiana's reputation. They held it in Brown County State Park in southern Indiana, which has ridiculously sharp short climbs. A few guys managed to buy climbing gears at the local shops after seeing the course. The rest? Many of them DNF'd.