Seems counter intuitive, but a 2x4 has a higher rating than the same vehicle in 4x4 because the extra hardware is extra weight
on essentially the same frame, engine, wheelbase, suspension.
Personally, I find that while 4x4 is not of much use on highway pulling trailer, it IS of great value when backing or starting on rough terrain in CGs. The tow limits are for highway, not bad back roads. Here I mean the 4x4 with access to 4W Low, not AWD.
Some models are apparently easier to abuse than others although the underlying vehicle might be almost identical. UHaul
won't let you tow trailer with Explorer but will with Ranger, although they are essentially the same vehicle until later models because of their experience with the tire-rollover problem and the difference in recommended tire pressures.