Steel cards make you stronger when youre challenging your opponent and dealing more damage
While it isn't game breaking, playing Naban, Dean of Iteration on Turn 2 into Sunscourge Champion on Turn 3 to gain four life is a nice value start for a Naban deck, especially considering that Sunscourge Champion can come back to gain eight life later in the game thanks to eternalize
It's strong in ETB heavy brews like midrange and blink, sacrifice brews where you can sacrifice to something like Attrition and then come back, Aristocrats where you can trigger Blood Artist for wins, life gain for lifelink shenanigans, Voltron and equipment that invested in equipment infrastructure to and any heavy creature build
So, why worry about how to block it or how much damage its going to do when you can simply destroy it instead
Printing sleeves isnt easy or cheap, and so there arent many places that do it
Or mill them and pick the best of the lot