How much can Jeep Wranglers tow?

Good info to have and something I hadn’t considered when I impulsively purchased my Jeep. It doesn’t have the towing capacity of my crossover (4,500lbs) but I never tow anything that heavy anyway. Looks like it’s plenty capable of handling a small trailer and 4wheeler, lighter camp trailer, etc.
 
I compared my 2013 JKU with 3.73 axles to a 2013 Grand Cherokee, both with the same motor and A/T:

JKU 1.2 inches longer wheelbase
GC 2.2 inches wider track
JKU has a Dana 44 vs IRS on the CG
JKU is 235 pounds lighter

The payload of the JKU is 880 lbs, for the GC it is 1840 lbs
The towing capacity of the JKU (with 3.73's or higher) is 3500 lbs, the GC is 5000 lbs

Why does the Grand Cherokee have a higher towing/payload capacity?