While I don't agree with this agreement, I don't see any particular problem keeping the negotiations and drafts secret. I mean, the final deal is obviously made public (otherwise there would be no way of enforcing that countries abide by it), but I don't think the negotiators needs to disclose every thought they brainstorm. It would create a lot of public and political pressure on the negotiators and instead of trying to reach something that every country can agree on, they'd be trying to appease domestic lobbyists.