Back in 2015/2016 (on the 73N), I flew lots of 4-leg/4-day trips, I even flew a few 3-leg/4-days, with min layovers of 16-18 hours. One of my favorite trips was one leg to SAN (from DTW), 18 hour layover and one leg home. Those were good trips and they went away sometime in late 16/early 17. Now, they've added a DTW-BOS before flying to the west coast on day 1. Anyway, there's just so much subjectivity to this, but I'd bet it boils down to extremely high block days followed by short overnights. The trips may not start out planned that way, but end up that way due to the current reroutepalooza and chronic staffing shortage.