The whole purpose is to keep EX Trials alive throughout a given patch cycle. They don't expect players to farm 99 tokens all at once but over a 4-6 month span. Of course, people do. However, that isn't the intent. Reducing the number makes it harder for player later on looking to farm. Hades and Diamond were exception; the former due to its length while the latter because it's the last one of the expansion. Personally, I think they were testing Diamond's longevity and decided it didn't last long enough. Hence why weapon coffers will drop in Endwalker but you'll still only get a single token per kill.