Truth to be told, it's not just OCE. Every worlds out there have been shedding players since Endwalker release, and have continued to do so even with new patch releases.

I feel that with the FFXIV has peaked at Endwalker with the conclusion of the Hydaelyn-Zodiark arc (one can draw parallels to the release of Wrath of the Lich King back in 2008 for WoW) and it's just downhill from now onwards, which makes the release of new data centers and worlds even more confusing as it's just going to split the already declining player base even further.