So as the article states, most of the noticed effect is explained by Big East conference realignment into P5 conferences.
Using arbitrary endpoints, they arrived at the fact that non-P5+Big East are earning 3% less tournament credits than from previous dates.
Part of THAT is further explained by credit-earning teams who migrated into the new Big East and P5 by 2014 who are lumped in with that P5 + Big East number but who earned credits for the mid-majors before, like Xavier, Creighton, Butler, Utah, and TCU.
There were a total of 675 credits given out from 2014 until last year. TCU earned 1 credit, Utah earned 5, Butler earned 9, Creighton earned 4, and Xavier earned 12 in that time. That's 4.5% of the total number of credits.
Now, these teams may not have earned the same number of credits in mid-major leagues, but the fact that they accounted for 150% of the gap leads me to believe the effect is at least partially and likely mostly caused due to just the growth in number of the P5+Big East leagues.