ItsJustMe

You might, but there are both tighter clearances and a lot more force involved. If you have ice on the rims, and apply the brakes, you're pushing a round-shouldered, rubber pad against the ice, and there's a fair amount of springiness in the system. It just slips over the top.

If you have ice on the brake rotor and apply the brakes, you're pushing a square-edged, very hard metallic composite pad into ice that's on a thin hard stainless steel rotor. It'll tear the ice off in a single revolution.

Also, there's very little clearance between the pad and rotor; mine are adjusted to where I can barely see daylight between them, so probably 1/32". If there's more ice than that, it just gets ripped off while I'm riding, BEFORE I hit the brakes.

Also, rims have a lot more thermal mass to dissipate heat than a rotor does. Obviously the same amount of heat is being put INTO either the rim or the rotor to stop a given mass from a given speed. But that heat will make the rotor much hotter than the rim, so it'll stay above freezing longer. Since freezing rain really only occurs within a few degrees of 0*C, you don't have to use your disc brakes very many times an hour to keep the rotor temp above freezing, as opposed to rim brakes.