On PPrune I found:
The aircraft has been designed to account for that. (Simplistically,
the tail is over-sized to compensate for reduced effectiveness when
ice forms; it's easier/cheaper/simpler to make the tail a bit bigger
and take a weight penalty than to install a whole extra anti-icing
system on the tail, which is why that's the typical approach for
higher speed aircraft)
To me this makes sense, as the weight penalty for making the tail a bit larger is not as big as the weight penalty for making the wing a bit larger.
Another thing that is different between wings and empennage is ice build up on the wing near the engine could suddenly let go and end up in the engine and cause damage. To prevent the ice buildup, anti icing is used. On the empennage this is no issue.