Stainless steel tanks was invented by the milk industry, and started to show up in the wine industry in the 1960s.
Stainless steel tanks make great containers for wine because:
One benefit of using steel tanks, is that no additional aromatic components are conveyed into the wine, which allows winemakers to capture the true essence of the grape varietal, and create a more pure and refreshing type of wine.
Most winemakers use steel tanks to produce a stable and flavorful result, especially for white wines.
Airtight steel tanks can be difficult to use for red wine fermentation.
The colour of red wines comes from the grape skins, which have a tendency to float and on the top of the juice as a "cap" during fermentation.
Traditionally, workers physically pushed this cap of grape skins back into the juice, for better color, and better extraction of tannins.
With enclosed steel tanks this is not possible. Some innovations have been done, like mechanical punching down the cap, pumping juice out of the tank back over the cap, or rotate the tanks.
The methods mentioned above are not typically used for fine red wines.