To add to Apple Fanboy's comment: I would suspect how the drivers perform as part of the Friday and Saturday practice programmes also influenced the decision process. Consistency lap after lap is critical to get good testing data to evaluate parts/tyre compounds. (The story goes Nigel Mansell was challenged at this. He only could drive 10/10, and frustrated engineers trying to figure out if the new add-ons were any good. I have no knowledge this is true, however it does fit the Mansell persona charm.)
I’m not sure Mansell was fit enough to be that consistent - he famously had to delay his McLaren debut as he was too big for the car! Modern drivers are certainly fitter, but I would agree that consistency may be the key here. I think Norris and Sainz are impressing by their consistency this season.