Food needs to be cooked in high temperature at approximately 170–180°C (338-356°F) in order to bring out its best flavor. Iron is a material with higher heat resistance, and is also the one best-suited to storing and releasing heat.
In other words, not only is it able to store abundant amounts of heat, it is also able to release just the right amount of heat in order to bring out the best in most ingredients. These properties enable food to be cooked quickly at high temperatures, all without losing any delicious flavor.
And the greatest advantage they bring lies in the fact that the more you use them, the more the oil and metal mix together to make them work even better. Unlike teflon, which degrades after several months at worst and several years at best, a good iron pan that is properly cared for can be passed on from parent to child to grandchild and beyond, for decades and decades. They are not disposable tools meant to be worn out and replaced. They are tools that are meant to be cared for, that can be made into something better than they were when they were first purchased.