My hypothesis on sustainability of the wine rack is that These crates or anything that has to do with the storage of wines are reused and kept for decades. But this is pertaining to the use of wood. The unsustainable part is the use of raw materials like Iron or some form of plastics.
The reason for this is that Iron rusts faster than other elements. The reason is that iron is found in pure formations of Fe2 /Fe3 and this is why it reacts faster to Oxygen and other elements. Usually Oxides(Rust) are supposed to be a protective layer to not expose the rest of the metal, but Iron Oxides eat away at the metal and exfoliates. This can be a problem for durability and health.
Plastics Can be used for long periods of time because plastic only photo-degrades., but the process it takes to make and dispose of this material is so harmful to the environment.