It’s because ice has a connotation of freezing. Freezing is kind of what ice has to do in order to be ice, so like, if you’re going to freeze enemies, you immobilize them. You have to trade off power for the abiity to have CC. It’s logical.
Not saying ice can’t be a powerful offensive type in RPGs. But that’s often the kind of role it lends itself to.
Also do not forget that Cryo gets Ice Pike. One of the most spammable and reliable “STOP!” CC’s in the entire game. Pyro might have flame piller but it can’t do that. Flame pillar is Pyro’s only hard CC while Cryo has 3 ways to control enemies not counting ice wall.
Also, if you do badly want to do damage with ice moves, there’s always Elementalist with its powerful hail.
But yeah, a cryo buff would not be out of the question, I just personally really enjoy cryo’s identity as it is and love combining it with classes who can make use of the CC it provides.