I trust some NIT Bracketology person as much as I trust Lunardi's NCAA bracketology.
Ultimately, it's a committee that decides the at-large bids, based on criteria that changes (or weighted differently) every single year. Lunardi's track record isn't all that strong, but it's entertainment.
The NIT gets whatever leftovers are remaining. And that's heavily impacted by the number of NCAA bid stealers from mid-majors.