The reason it doesn't go bad is the sterilization/canning process, not the glass container itself. The jar of salsa was sealed and heated to the point any microorganisms inside the sealed jar were killed and the fact it is sealed means no new microorganisms can get in preventing spoiling. Properly canned food can theoretically be safe to eat indefinitely as long as the seal isn't broken and it's kept somewhat cool though the texture/taste can definitely degrade.

Glass jars are just a convenient container for canning food in, but are not doing anything special to prevent spoiling.