It wasn't economically feasible, the owners wanted out, no buyers stepped up.

Numbers wise it was ~ 1.6 million tonne per annum in a global market that demands ~ 20 million tonne per annum, as a smaller producer in Tasmania with other factors dragging down it wasn't competitive with South Africa, Gabon, and Ghana.

Australia’s only manganese smelter to close, administrators say - https://www.mining.com/web/australias-only-manganese-smelter...

right - but in the context of this thread, manganese is a vital ingredient to smelting iron - so Australia seems it is no longer self sufficient.