My answer would be: because it's 2020.
It's a new world out there, and it's run on turbos and 10 speed transmissions. Yes, I realize power is hardly a factor in any towing equation, but my point is that design and engineering in all areas are making vehicles more capable than ever. I don't even try to keep up with it, but I recently looked at a GM trailering guide to see what it recommended for towing on my new 1500 without weight distribution and it said 7k. not too long ago 5k was the norm. I did a double take and checked my eyes to verify that it really said 35K gooseneck towing capacity on a 3500.
Is it a good idea? probably not in all cases, but i'll always factor frequency into the equation. If I'm towing more than 5k every day then I'll most likely opt for a 2500 or more, but I can't swing a dead cat without hitting half a dozen contractors putting 50k a year on a 1500 and towing a 5-7k enclosed cargo everywhere they go. They can't all be wrong. If I'm only occasionally towing a camper or tractor or whatever, i would also not worry about being at the manufacturer's rated max as long as I felt safe. not everyone here is towing their equipment every day, and there's a fine line when you need capacity and also a daily driver. I've seen a few on here over the years that go so far off the scale in the other direction that they'll talk themselves into a C60 with a 24' deckover to haul a BX.
I had a brand new 2006 gm 2500 gas and it surely was no powerhouse. I truly believe that the powertrain in my 3.0 diesel would pull circles around that setup, but sure, i agree that the 2500 felt more stable, as my new truck reminds me of driving my living room couch at times.
