Speculation is that Kimbrel is now the closer and last night's game didn't provide an opportunity for him to close.
Yes, that's certainly my take from yesterday, as I'd posted earlier. For weeks Jeffress has been 9th inning, with Kimbrel pitching 8th with modest leads. To my recall the only other guy who's been used in those situations has been now-gone Wick. But yesterday with 2-run 8th-inning lead, in what has been a Kimbrel inning, Ross instead went to Jeffress. Pretty obvious that Kimbrel was going to pitch the 9th, prior to the Cubs padding 3 extra runs on.
deeg is right, Wednesday's outing is Kimbrel's only appearance in ten days. Since Wednesday, opportunity hasn't matched Ross's usage plan. Thursday off; Hendricks went 8 on Friday, and Ross hadn't reversed the Kimbrel/Jeffress roles yet then, so Jeffress still got the 9th on friday. Then Sat and Sun were losses. I'm guessing it was after Friday night's game that Ross made the decision to flip the roles. I kind of resonate with deeg's thought, that sitting Kimbrel too long is iffy. Wildman is his risk, so when he comes into a tight save situation, with all the adrenalin rushing, and without having pitched since Wednesday, that almost heightens the risk that he'll be so over-amped that he'll overthrow and revert to wildman and make everybody nervous again. Hopefully the Cubs are positioned with a save situation tonight, and he's able to locate and make it non-stressful.
To some degree I think Ross's overall handling of this has been reasonable. he didn't lock into Kimbrell and force him to keep pitching save situations even when his mechanics and confidence were unready. He never announced Jeffress as closer. I think in retrospect it was wise to take it slow with Kimbrell and let him stack some successful innings. And I think it's wise, too, that he's not locking onto Jeffress as closer, and isnt waiting for some dramatic blown save to make the switch. With playoffs approaching, Kimbrel will maybe get a couple of save opportunities first, and might then be positioned to be effective in playoffs.