Charles is Ferrari's current poster boy. They will give that man the number 1 seat over Sainz who's continuously improving despite being shadowed by Charles at most times. He's a great driver that can go very aggressive against better teams, and I believe he will do even more if he's in a team with a better car as the number 1 driver.
There aren't a lot of many good teams with a good car that is better than Ferrari right now, and it'll be tough for them to choose Sainz over their boys even. I just kinda wish that the red guys will see Sainz more than a 2nd driver, as he's been very consistent for quite some time now while Leclerc is always struggling to get better placement not until Sainz comes in for help.