Did you miss the below quote from the linked article?
"...After the Hartford proposal fell through, Robert Kraft paid for 100% of the construction costs, a rare instance of an NFL owner privately financing the construction of a stadium."
Concurrently announced was a new road to access the stadium from U.S. Route 1, and an additional 3,000 parking spaces to accommodate the increased number of fans.. In other words the stadium is only part of the total construction costs. But, politically indirect costs where an easy sell.
"...After the Hartford proposal fell through, Robert Kraft paid for 100% of the construction costs, a rare instance of an NFL owner privately financing the construction of a stadium."