Red Bull just ran their expected strategy and for some reason Merc shat the bed over track position. Verstappen may have won either way but still, that was very odd. It's not like something happened in the race that would have been a logical trigger to switch to the hards either. I guess they were just obsessed with Perez not gaining track position on Hamilton which is what would have happened had they stayed out longer. With the lack of straight line speed they were presumably concerned they would not be able to overtake Perez on track.
Maybe medium to hard was always their go to strategy.