I'm not the guy when it comes to the NIT. I only start watching March Madness (except for UT games, usually) around the Sweet Sixteen. March is too beautiful usually to watch ball all day.
I just trust ESPN to look for more and more games to televise that make money. They'll play up this "someone good gets left out of the CFP" discussion as much as possible to try to justify 16 teams ASAP. It's good business for them.
I think the G5 or NCAA or the money is stopping a "one step down" football tournament. Which one(s) would only be a guess for me but my guess is: money, NCAA, G5 in that order.
Admitting you're not worthy of the top tier tourney would be hard for the G5, I think, but money makes things hurt less.
The NCAA wants to avoid as long as possible the split of the high revenue programs from the low revenue programs which 2 tournaments implies. The NCAA will probably be abandoned by the high revenue programs in favor of some kind of new organization which will cripple the revenue the NCAA makes.
ESPN simply won't do a lower level tournament if it's not going to draw enough ads. That kind of market analysis should be their bread and butter. If it were very profitable, they'd push hard for it.