If Ferrari pitted both drivers they could not control the front with 2 cars. One pass and they'd loose the race.
In that SC situation they choose to maximize the chance to win and they did win.
Leclerc was getting the lemon deal though imagine Sainz getting pole, Leading, being asked to give Leclerc the lead and then being sacrificed in the SC situation.
A clearer nr2 statement is hard to find. They have 2 top drivers and need them both to perform at their peak.