I believe the lack of a commitment by Delta for such a project is twofold:

1) Delta would need to empower MAC (Minneapolis Airport Commission) to organize and execute such a project. History has shown an abysmal track record of Minneapolis airport improvements for even the simplest tasks. I imagine that in the eyes of Delta, this would likely lead to a cataclysmic failure of epic proportions unlike anything experienced in the history of the world. At least leaving it as the **** sandwich it is now, Delta keeps that variable quantifiable and in check.

2) Minneapolis will likely see a financial downturn as it has one of the highest corporate tax rates in the country. The number of Fortune 500 companies within the state are dwindling as time passes. My guess is that Delta is taking this into account with the decision to go ahead with the new terminal. They don't want another Cincinnati.