The cooldown is designed to gate use to encourage players to engage in face to face transactions. Trading is not intended as a tool, but a feature to be used as needed. This also prevents players from camping monuments and being able to trade items to a teammate for storage.
Expected usage: DOH!, I forgot my axe at my base, can you trade me one?
Expected usage: I'm dying of hunger, can someone help?
Unexpected usage: I'm selling an axe, trade me
Unexpected usage: My inventory is full; let me trade you so I can keep farming
The 5-minute cooldown was set in place to get players used to having a cooldown, and will eventually be increased. With the new system, the trade is not over once you click accept. As long as both players stay in the trade, you can trade as many items as possible.
Additionally, we do not advertise trade as part of our rich player economy. It's listed as a feature.