Why does carburetor icing require manual attention by the pilot?
Not every motorized engine is the same: For example, you would be hard-pressed to find a carbureted car these days.

The most similar kind of land-vehicle engine you'll find would be a motorcycle engine, and those do in fact suffer from carburetor ice:
- A discussion of carb icing on the Ninja 250
- A thread about carb ice on Bike Talk Forums

Older cars with carburetors were also susceptible to carburetor ice, and eventually included measures to avoid or mitigate it.
This could include passive changes such as mounting the carburetor in a warm part of the engine compartment (usually above the block, in a downdraft configuration), semi-active changes like "heat risers" which would feed warm air into the intake (usually behind the throttle plate, but occasionally in front of it), or fully-active systems like automatic "heat flaps" and "Time/Temperature switches" which do the same thing as the carburetor heat control in an airplane but without the driver's input or control.

These systems aren't usually fitted to aircraft as they add both weight and complexity, and can come with their own disadvantages (such as reduced power if the carburetor heat flap is in the "on" (heating) position during takeoff or on a go-around).



So why don't we hear about ground vehicles suffering from carburetor ice as much? Three main reasons:


Carburetor ice is most likely to form at low power settings.
Your car or motorcycle probably doesn't spend much time at or near idle power unless you're stuck in traffic: A few seconds coasting to a stop and then you accelerate away again.
Carburetor ice is less dangerous when you're on the ground.
One of the most common times you'll have a carburetor ice problem is during an approach/landing, with the engine at or near idle power for an extended period of time (this is why many aircraft call for carb heat during landing). Having your engine die at this point is a pretty serious problem, especially if you need to execute a go-around.
The analog in a car or motorcycle is having your engine stall after spending an extended period idling (standing or stopped in traffic). Having your engine die when you try to accelerate away is inconvenient and will probably make other drivers honk their horns at you and say unkind things, but it's unlikely to kill you.
There's nothing the driver can do about it.
A driver doesn't usually have a "carburetor heat" handle to pull (except possibly in very old cars), so you can't turn around and say "Your engine stalled because you didn't do this." On top of that because the problem is usually more inconvenient than dangerous on the ground it's not likely to make news: "Driver had to sit on shoulder for 30 minutes while their carburetor thawed out. Hundreds inconvenienced by rubbernecking traffic." is simply not as newsworthy as "Airplane crashed!"