There is reciprocity though. Direct buyers, and those grandfathered, may stay at Riviera just like direct buyers of Riviera can trade into other resorts. Newer resale buyer can't trade into Riviera however resale buyers at Riviera also can not trade out to other resorts. There are limitations going both ways.
That isn't reciprocity because it doesn't prevent the resale home resort owner's interest being used by another member whose interest the home resort owner doesn't have the right to use.
It's a difficult concept to get one's mind around, but as a starting point, the way a point based timeshare works is that each person has a real property interest in their home resort. They can choose to, instead of staying at their home resort, put their points in the network's bucket and use someone else's points. (I realize this sounds like the RCI exchange but really the DVC network is a simplified version of that.)
Disney's new resale restrictions allow a direct Riviera owner to use a resale owner's points and bar that resale owner from using the RIviera owner's points.
So, your likely next argument would be, but there are other points in the bucket!. To which I would say, how is that guaranteed? As the future resorts come online and the 2042 resorts go offline (to most likely become future resorts), the availability of points to resale owners will become more limited, but those resale owner's points can still be used by these future owners. In other to ensure the integrity of the system, DIsney would have to earmark member's points based on their resale/direct status, preventing future resort owners from using resale owners points. While this may be theoretically possible, the complexity would make the system impossible to maintain.