Why so secret?

Once a month or so I see a story about the Trans-Pacific Partnership.  Each of the articles points out the secrecy of the talks by the participants; not even Congress is involved, although corporations and trade associations are.  Each is down on the trade treaty for several reasons: consumer safety, environmental practices, intellectual property protection, financial industry deregulation, egregious patent extensions, etc.  Now the articles are about loss of jobs.  Yet, the day when this treaty will be signed draws closer.  I wonder why Romney has not mentioned it as it is another example of poor judgment by the Obama administration.