It's because you have no tradeable keys in inventory. Steam has newly paid for items being untradeable for a week.

Your keys in your inventory show as "Tradable After: Wednesday, November 04, 2015 (8:00:00) GMT"

Valve added this to reduce instance of card fraud I believe. They guarantee trades done in Steam window, so they can't remove items if first purchaser chargebacks. Yeah it sucks. Like many things on Steam, all due to scammers. Steam support hardly duplicate items back (which they used to do) when you fall for fraud, I believe because scammers would fake fraud and have their items duplicated when they remained in control of both the "stolen" and got new duplicated items restored. Valve also can't delete items after a few trades because it would make it unsafe for customers to trade on Steam if there items could be removed after a trade because a scammer traded them to you/frauded Steam. Hence duplication, which they no longer do.