Thanks to TeryT's post on the Open Roads Forum, the following response was provided by Jim2Public2:
"The stock hitch supplied on all 4-Runners has a very short tube to clear the spare tire and not protrude beyond the rear bumper. It also doesn't affect the rear crumple zones in the 4Runner.
Toyota restricts the hitch to 5000 pounds and 500 pounds of tongue weight, no WDH permitted. They also forbid the use of extended drawbars due to the excessive leverage imparted.
For the full tow rating you have to get an upgraded hitch. The upgraded hitch will end up protruding behind the rear bumper similar to the hitches on the Nissan Xterra. It will also attach to the main frame rails which could affect the rear collision safety.
By not offering a stronger hitch from the factory, Toyota avoids the possible negative impacts in rear end collisions and the problem of having the hitch extend beyond the rear bumper, a possible liability issue. I don't blame them for not offering the stronger hitch; at least they have a full tow package with trannie cooler and electrical wiring standard. If I bought one it would be a minor task to bolt on a Hidden Hitch.
Many vehicles with a tow rating don't include a hitch at all."
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As Canadian vehicles have different safety standards than US vehicles (such as requiring daytime running lights since 1990), and I believe the Canadian vehicles must withstand a higher bumper impact that the US models, Toyota may not want to extend their hitch beyond the bumper. Although the manual states that V8 models are good for about 7,000 lbs, with proper additional equipment, Toyota does not provide the higher capacity hitch, as it appears to protrude beyond the bumper.
As the hitch does help to reduce people driving into your vehicle, I may consider a Hidden Hitch, but don't expect any help from Toyota, due to their potential liability interests. This same rationale applies to my winter steel rims without tire pressure monitoring, as it defeats the safety purpose of the electronic monitoring