Like others have said, the mid majors used to thrive because they were experienced and had a huge experience advantage over the one and dones. Now you have Kentucky, Michigan, Florida, Michigan State, Duke and Arizona just taking those experienced guys. We'll still get a Saint Mary's, Drake or McNeese State occasionally. But the mid majors of our past have all been added to the list of "should be good". Creighton, Butler,Xavier and Gonzaga aren't true mid majors anymore.
They can now miss in recruiting and still get the diamond in the rough they overlooked a few years down the road. This is how Michigan, Kentucky, Florida and Arizona were able to build themselves up so quickly under new regimes. It's why Indiana will be a contender next year. If you can't make the tournament when you have every advantage handed to you, you really really are terrible. I'm looking at you Ohio State, USC, Florida State, Virginia, Miami, Arizona State and Notre Dame. Heck I'm looking at Iowa, Penn State, Nebraska and Minnesota as well.
Let's just say the entire SEC and B1G conference at this point.