That's because some of those Kia engines are high compression. If it has a turbocharger, that increases the compression further because the turbocharger forces air into the cylinders under pressure.

You don't technically have to use high octane fuel in those. The ECM (the engines computer) will adjust the timing to prevent premature detonation. However, doing so will diminish performance and fuel economy to the point where you're not saving any money by buying cheaper fuel.