Why doesn't JJC (copper ETF) suffer from contango?

So I understand futures-based ETFs will decline in value as they rollover front month contracts. But I can't understand why JJC (iPath Bloomberg Copper Subindex Total Return Sub-Index ETN) hasn't been affected by contango which copper futures persist in. The OIL ETN (literally "OIL") by the same ETF provider underperformed spot WTI prices when oil was in contango. Why isn't JJC affected by copper contango?

EDIT: Copper futures curve Futures snapshot

EDIT 2: WTI spot and OIL versus copper spot and JJC.

Submitted January 22, 2018 at 09:21AM by IvanLu http://ift.tt/2n3eDUC