Canning was unsustainable because the process back then was labor intensive; the process was still undefined, and the materials are very primitive. The cans used were corked and sealed with lead which led it to be hazardous
Those challenges included fishermen catching more fish than the canneries could process which means a lot of it went to waste. And some areas were actually overfished and resources began to run out, which meant this was an unsustainable system.