For the same reason why big-bang, throw-code-over-the-wall open-source projects rarely succeed.

The flawed TPP process will affect 800 million people.

At the very least it makes for an extremely boring discussion if we start from the premise that the article must be right "because lobbyists".

Non-inclusive processes don't fail because of lobbyists. They fail because the excluded majority ignores outputs which made little attempt to include their requirements. A poor process that creates non-representative TPP law will degrade public perception of future laws. See the movie 1776.