Yeah, if you read the Korean language article[0] (or the Namu.wiki article[1]), they both refer it the function as preserving and storing kimchi, not really going for further fermenting. Most folks I know buy prepared kimchi and use the fridge to store / have it last a while (as well as using it as a secondary fridge). Given that optimal kimchi ripening goes from 2d to 35d changing the temperature from 20°C to 4°C[2], I suspect it would take an enormous time trying to ripen it purely in the -1°C fridge (typical kimchi fridge temperature).