Yeh, as Old Fella says, the key to carb heat is the venturi in the carb. Ice in the venturi disrupts the airflow and the fuel is no longer sucked in as efficiently, just as ice disturbs airflow on the wings. Same thing, only different..
Carb heat, in all the lightplanes I've seen, takes heated air from a muff around the exhaust pipes. If the engine dies from carb ice, you're no longer generating heat in the exhaust, so your prospects for a re-start are reduced - a lot.
Injected engines, have no venturi in the intake, of course, just a butterfly throttle, so icing isn't a problem, except when the intake filter gets clogged with it. Alternate air is just that.
GB