I'm not sure what the reasoning is for not allowing the socket punch recipe to work on any item, but the RNG is bad enough trying to craft an item without it. I'm playing a melee necro and trying to farm for upgrades but I'm 128 and still haven't found a single usable chest better than a tiered unique (werecat). Finally decided to try and craft something better and so far I've gone through multiple full inventories of renewal potions just trying to get a good base item to use but there have been so many good rolls that have 1-5 sockets that make it worthless.
Now, I could see if crafting was useful for early game so there would be cases where having 1-5 sockets would be ok but crafting is exclusively a mid / late game thing where you need 0 or 6 sockets to have something even remotely usable. I don't see any reason why socket punch shouldn't be usable on an item that is already socketed so that at the very least I'm only trying to pin down 2 attributes on the thing rather than 3.