Duct tape uses a rubber compound as adhesive. This rubber is vulnerable to everything that attacks or weakens rubber. Heat, UV light, ozone, normal atmospheric oxygen and petroleum vapors destroy the adhesive. This is one of the reasons why one thing you never use duct tape on are ducts. When the heat kicks on it isn't long before it starts falling off. It is also why even in ideal storage situations it degrades in time.

All duct tape degrades with time. Good contractor and military grade duct tape degrades more slowly for any set level of abuse during storage. Cheaper stuff goes south much faster. The cheapest discount store stuff, that has been on the shelf for years, may be useless right out of the wrapper even if stored under ideal conditions.

The ideal storage conditions are cool, dry, away from strong light, heat, chemicals and their vapors and well away from electrical gear, like motors, that can create ozone. But even under ideal conditions high quality duct tape will deteriorate in time. Stocks need to be rotated and either used up while it still works or discarded.