It is not because of simple retro taste, but the science of heat is working here without knowing it.
There are three types of heat: conduction, convection, and radiation. Gas fire and charcoal fire are different from each other in the transfer of heat. Gas is convection, and charcoal is radiation. Compared to convective heat, in which heat evaporates moisture on the surface of an object, radiant heat that spreads in all directions plays an important role in maintaining appropriate moisture by emitting far-infrared rays while distributing heat evenly on the same principle as solar heat.

The experiment was conducted with a gas fire and a charcoal fire lit 12 cm below the meat, respectively. Charcoal fire-grilled with radiant heat raises the temperature almost twice as fast as a gas fire, simultaneously raising the temperature inside and outside the meat and melting the protein and fat on the surface to form a film.

As a result, the moisture inside has a steaming effect on the inside, making the meat tender. Charcoal fire, which contains a lot of far-infrared rays, is a heat source where the temperature rises ideally. Charcoal is 72 degrees, but gas is only 23 degrees.

Because of this characteristic, when grilling directly over a gas fire, not only the moisture on the surface of the meat but also the moisture in the meat evaporates and becomes tough.