Why does the PDGA calculate ratings based on the scores propagators shoot versus using a fixed course rating like ball golf?

How would you calculate a fixed rating for a course layout simply by taking measurements, looking at foliage, fairway widths and accounting for hazards? It’s also common for TDs to add temp holes, change tee or pin positions, or use new permanent or temporary courses such that no course rating would be on file to use for that layout. Then, imagine trying to calculate and keep track of those layout ratings on courses with dual tees and 2 or more pin placements per hole that can produce thousands of configurations. Using the scores of propagators with established ratings to produce a course rating for each round has proven to be an effective way to indicate how the course played that round automatically taking all variable factors into account such as number of holes, weather, lighting, time of year and tournament pressure bundled up simply as each of their scores for the round. Having more propagators provides more measurements and improves the accuracy of the numbers. Ball golf uses fixed course ratings for their handicap system. Fortunately, they only have 3 to 5 configurations to track on each course. Unfortunately, weather and tournament conditions cannot be accounted for with their fixed value system.