The last "official" Jewish commemorative day was added 2000 years ago. Why can't there be any new ones (approved by ALL), considering all that's happened to Jews since?
Jewish communities have local commemorations. In Egypt we had Purim Mitzrayim, to commemorate a narrow escape in 1524. But it is not the case that the only "official" commemorations that apply to all Jews are those commemorating times when all Jews lived together in Eretz. At the time of the fall of the Second Temple (last "official" Jewish commemoration), there were large communities in Alexandria and elsewhere in the Roman Empire, and in Babylonia.