Noise reduction is a very well-understood concept. You record your sound, then invert the resulting sound wave, then play it back. The slower they system plays back the inverted wave, the less effective it is. These days we have the processing power to play back the inverted wave near-instantaneously, so that's not an issue. This works with sound of any frequency.
The problem is that you don't want the noise cancelling technology to cancel out your music or your conversations. How do you isolate those sounds out? With music, the car can have knowledge of the audio coming out of the sound system and subtract out that part of the recorded wave before inverting it. But the car has no knowledge of your conversational audio. So the best it can do is allow a pass-through of typical human voice frequency, which is a pretty wide band. Which means any road or wind noise in that band will also pass through.