Because the newpaper's classified is mainly read by the unemployed. Those who need to find a job because they haven't been able to get one.
Radio reaches people everyday at work, going to and from work in their cars and at home before and after work. Your radio commercial is much more likely to reach employed people ready to consider an even better opportunity than the one they have.
And radio doesn't stop at the city limits. An employment ad on KZOR reaches Hobbs, Eunice, Jal, Lovington, Seminole, Denver City, Plains, Andrews and beyond.