Ilford and Kodak and other manufacturers used to have large, well resourced testing departments - sufficient to permit them to do value added things like testing other manufacturer's developers with their films.
Now, with those resources being so much reduced, I expect those value added services are just not practically possible, at least not at a cost that would be justified given the effects on sales.
In addition, in days gone by, there were no resources like the Massive Developing chart - people were forced to rely either on their own experience, or manufacturers' printed materials. In today's world, where many people seem to go first to independent internet resources, without even glancing at what the manufacturers suggest, it doesn't surprise me that Harman has elected not to do that testing work and share the results.