They knew what Gerald had done to him and there were whispers here and there about his infertility because Iris had not yet conceived.
Moreover, Cane didn't need to explain where he had gone that night, the very night he was supposed to spend with Sofia.
Jace knew that Cane also noticed, by keeping Sofia close and not revealing the fact that the baby was not his would put Iris in a difficult and uncomfortable situation. In addition, with this, they could buy some time for themselves to strengthen their stronghold before everything went down.
Because if the Alpha's infertility was exposed, the King would see it as a chance; as there would be no reason to let Cane be the Alpha of the pack anymore, since that was the same reason Cane used to drag down Mason from stepping up to the Alpha's position, pinpointing he couldn't have an heir of his own. That was how important an heir was for someone like him.
