I think profit is part of it, but I think that people running multinational corporations with more money than they could spend on themselves for the rest of their lives if they tried would have interest in shaping law indirectly via the supranational tribunals that are part of these trade agreements.

There are other reasons besides money that people get into politics and this would allow corporate owners to directly manipulate politics for monetary and non-monetary reasons without having to do the whole lobbying and/or running for election thing.

I think that profit is a cop-out when it comes to understanding political motivations. Ideological motivations are real and not merely a cover for monetary profit seeking behavior. There's this assumed idea that we live in a post-ideological era and that all decisions are pragmatic or at worst, motivated by profit seeking. I think ideology is still there, but in our dumbed down world it's never explicitly mentioned as a motivation for anything except as a vague throwaway line (e.g "Let's Make America Great Again!").