With a month or so before the season this is a negotiating ploy. The Seahawks are experienced, skilled financial negotiators. Adams, (as a negotiator), is an inexperienced, egotistical, blow-hard, who will no doubt complain about unfairness and anything else he can think of. His best card was to force an extension during his 4th rookie-deal year when his valuation was at its highest and his, (potentially lost), pay was at its lowest. He has wasted that opportunity. Financially Adams is in a weak position facing a 5th year option - tag - tag scenario, a below market value extension, or a hold-out in which he'd lose significant money.
It's not risk free for the Seahawks. It strengthens the negotiating hand for other players who might be tag targets and it doesn't put the Seahawks in a good light with potential future free agents. However, over a long period of time the Seahawks have shown themselves to be amongst the NFL's elite when it comes to contract negotiations and you can't win at poker if you aren't willing to bluff and lose a big pot.
Adams is a very good player. I'm not his biggest fan. He deserves an extension. I'm not surprised at the current situation. I think it gets resolved by Week 3 latest, (assuming Adams' ego doesn't get in the way).