I guess their thinking was probably that they have big enough car margin that they can do two runs, minimizing chances of a mistake affecting their lap. It almost worked as Norris was probably on for pole before his late mistake.
I am not sure I agree with the idea, it means that your first lap will never be as fast as it could because you carry more fuel and you are running earlier in the session. Going late was obviously very beneficial as the track improved at the end of each session. Doing only one lap would carry the risk of your mistake affecting your lap, but it would also give them a bigger margin to make a mistake, any minor mistake would be fine.
But at least we'll get a fun sprint tomorrow and then we can reset for the qualifying. I expect more in qualifying and the race.