I suppose this really is a lot about psychology, and also about the rhythm and structure of the race.
I think there was this one stage where everyone was chilling, apart from that there have been no easy stages for the guys who in other GTs would have some tough target days and many ones where they can't relax totally, but ease a bit, nonetheless. Here they can never ease. It started with that crashfest in Nice, and since then the amount of mountainous stages, the battle for green, and the amount of road furniture on some stages has produced a lot of stress and the need for the lighter guys to ride a high tempo on the flat.
Then in the beginning the quality of the riders at the start was extremely high and some of them were in really good form, so the pace up the climbs wasn't easy and must have felt even harder for those who were not at 100%. Had they been at their best they would probably have seen that the climb they were going up so fast came after a relatively short and easy start to the stage, also it might have been a bit cooler than for instance last year, but since, with their fatigue, the beginning did not feel easy, they could point at the climbing times and say "see, here, the numbers are high".