Why don't airport have heated runways to deal with winter conditions?
Removing snow from runways is not the biggest problem. Snow can be ploughed from the runways pretty quickly. The problems occur:


When it is snowing, especially in snow storms with strong winds and poor visibility. The wind and visibility are bigger problem than the snow laying on the runway and when the snow fall rate is such that the snow becomes a problem itself, the heating system would not be able to keep up melting it anyway.
Due to snow and ice accumulating on aircraft preparing for take-off. Obviously heating runways would not help in this regard.
Due to fog, which is much more common in winter. Again, heating runways would not help in this regard.


So runway heating would probably not help very often.

Also the runway has to be extremely strong, because aircraft have much higher weight on each tire than cars. A heating system with adequate durability would therefore be really expensive.