I hear you - it's sad to see extra parts in some setups that end up being thrown away because they're not needed. When I originally bought it though, I recall reading that there is a stop, but it was not very clear that the stop wasn't included if you bought just the hinges.... I wouldn't have minded to pay a few bucks extra to have it added. Anyways... it's been years and I didn't need it till now, though I always have been careful so that when the gate was opening on a slope it wouldn't swing out too hard and far out. That was the reason for needing the hinges in the first place - the factory one overtraveled pulling the stop out and damaging the gate in the process. Wasn't too happy as the dealership too nearly 2 weeks to fix something that was a "shortcoming" with a stock tire causing it to overswing....
There is a well known problem with some JK Wranglers in which the tailgate retaining strap over extends and comes out of its tension mechanism. Jeep has issued Technical Service Bulletin TSB #23-022-14 Rev A, dated October 23, 2014 regarding this issue. One of things that TSB calls for is replacing the hinges with a later revision. And a revision to that original TSB was issued on 9/5/2015. I don't have a copy of the later TSB but I believe it calls for the hinges to be replaced with an even later revision of the hinges.
Jeep has issued several revisions to the tailgate hinges over the years to try to compensate for the poor tailgate retaining strap rod design. The black hinge in the foreground is an early hinge, the red one is a later version, you can see how the early hinge opens further than the later version. There are even later versions than the red one, because the problem can still happen with the red one (from a '13). The TSB calls for installing updated hinges as part of the fix.
The TSB is entitled "TAILGATE RETAINING STRAP OVER EXTENDS AND BREAKS", but in fact the strap isn't broken. I posted a video in 2016 showing how the strap can be popped back into place.
The screwdriver is used to keep the stay rod centered in the opening, without it the rod will hit the nylon side guides in the opening, which will prevent the rod from going in. It takes a pretty good amount of force with the screwdriver to keep the rod centered while you're gently but firmly closing the tailgate. Don't rush closing the tailgate, when the rod is properly centered and there's enough force from the tailgate, the rod will pop back into place.
Even though the strap is easy to pop back in place, it'll pop out again unless the hinges are updated.
The MORryde hinges are designed to open just far enough to prevent the retaining strap from pulling out. The reason for the stop is that when the hinges are installed with the MORryde tailgate reinforcement, because the reinforcement is sandwiched between the hinge and the body the tailgate can pull the strap just a bit further and that can cause it to pull out. For that reason the stop is only included with the tailgate reinforcement.