Each time the criteria/process was a bit different, and if I am remembering right it was about a year that each one lasted. The specific reasons why it stopped I am sure vary and only NRC knows the exact reason, but for at least one of them they were missing out on candidates with really good test scores because they didn't fit the matrix they had, and then the remaining spots were very competitive.
Historically selection rate is 50% so if you auto select a bunch of applicants that doesn't leave many other spots open.
The PA's do change every few years and sooner if needed, which means they can adjust this as necessary.
This process does make sense to me to a point, especially when you see that historically those with 8's and 9's and no waivers are almost always selected. If I had written it I probably would have set that bar at an 8 rather than 7.