I mean, I think the word 'corruption' is being over-used here. But discussions about say tax rates or agricultural subsidies follow the normal legislative process. Do you feel like these issues are being handled optimally now? It just gives a huge attack surface for lobbyists and rent-seekers to complain and whine and get their way.
If the trade deal went through the 'normal' legislative process, every rep with a bit of leverage would hold it hostage for the pet industry or major employer in their district. "I won't sign off on this bill until we have a special carveout for Local Industry!" etc. etc.