I agree, I have no idea what my TJ did. It was the 2.5L/5-speed manual with 4.10's. I didn't buy it for the fuel mileage (and that is a good thing...).
Now my 2021 Unlimited Rubicon is bone-stock, with the 2.0L Turbo/8-speed automatic, and I LOVE it. Wifey and I putzed around yesterday after a fill-up with all pavement, but some very curvey mountain roads, and exploring a state park at 5 mph. Gained around 3000' in elevation too. Still got 22.5 on the trip computer, which I have found is pretty dang accurate for me. Did I mention I LOVE my Rubicon?