this was previously noted in https://forum.inaturalist.org/t/user-with-many-species-is-excluded-from-stats-if-not-within-top-200-observers-in-traditional-project/42912/6 and https://forum.inaturalist.org/t/im-missing-from-the-global-leaderboard-observers-by-species/60401. staff have not commented specifically on this, but i believe the behavior is intentional (though it’s not great in my opinion).
it’s possible to get the correct list using other means: https://forum.inaturalist.org/t/cutoff-for-2023-top-500-exceeds-6-000-observations/47901/27.