I’ve often wondered about this sort of thing. (XC and gnarr)
You could argue that fitting grippy tyres and a dropper would mean they can all ride the sort of stuff we enjoy when we go out for a mess about on our bikes.
But they probably figure fast rolling light(sketchy) tyres plus carbon post set up for pedalling efficiency means they smash the climbs and flats and mince down the techy bits.
Overall one climb is worth ten techy drops in terms of time gained.
When I watched the XC Olympics I was shocked at the riding. One third were brilliant but one third were pants at the techy stuff. Quite a few were removed by the sweeper and never did more than one or two laps. Some walked the descents on the first lap ! Sure, the winners were brilliant at everything, but they were the exception of course.