What's the advantage of a pre-built stove/fire/barrel?
A benefit of stoves is that they have six cooking slots compared to the camprfire's two cooking slots, allowing you to prepare more food quickly.
Likewise, stoves and other contained fires are found indoors or covered areas where you're sheltered from the elements and can search for supplies while your food cooks.
The third benefit of permanent cooking fixtures is that fires created in these can not be blown out, unlike a crafted campfire which is vulnerable to the wind and weather.