Better thermal conductivity (cast iron actually sucks at this but nobody seems to acknowledge it)
One of the main selling points of cast iron is the fact that it has low thermal conductivity - it takes a while to get hot, but then it stays hot for longer. This is an advantage for some types of cooking and is why I only use my cast iron for specific things.
Fwiw, I agree that if you only have one pan, don’t make that pan cast iron - it’s good at what it does but it’s not as versatile as a stainless steel pan for most things.