... or just applied for one? Do you know?
From what I understand to get a patent one has to make a discovery that no one else has done to date.
Smelting requires heat and any source should suffice.
So where is the discovery?
If I use gasoline or a laser for example, to raise the temperature have I made a discovery that deserves a patent?
I suspect not.
So why have others not used gas to smelt? I suspect because it was more convenient i.e. less expensive, to use other means. Only when one method becomes prohibitive that one switches to another.
Fortunately I do not have much mining and smelting knowlege to answer those questions, other wise I would protest a limitation of any heating method to a single entity.