Carbon reduction is not used to obtain certain metals from their ores because
1. Carbon cannot reduce certain oxides, sulphides, etc
2. It can react with the metals to form carbides
3. Temperatures required for the reduction are too high
4. It is expensive compared to the alternatives for some ores

Reduction by carbon (Smelting) : (This is common method of reduction)
"Reduction of the oxide with carbon at high temperature is known as smelting".
The oxides of less electropositive metals like Pb, Zn, Fe, Sn, Cu etc. are reduced by strongly heating them with coal or coke, in the blast furnace.
Slag : Fusible metarial during reduction process.
Slag : Gangue + substance (for remove gangue)
Fluxes : Substance used for removing gangue
But sometimes carbon reacts with metals and forms carbides so it can not be used for reduction.