Exactly this. We have no way of charting retention with any kind of statistical precision without having access to activity data logs and in turn whether the content met some unknown threshold of (sustained) activity or longevity that would likely be irrelevant to the devs' decision-making anyways.
We dont have that metric..but SE does.

I will hazard a guess that this may be why we didnt see a zone like that for Endwalker.

This is no more than speculation, but it MAY be that SE decided to give exploratory zones a pass for THIS expansion, but it may appear in Dawntrail? None of us know what the devs decision making process was, but again ( and I am operating on the proviso I dont know for certain ) it may be possible that they held off, with plans to include it in the new expac, since Endwalker would already have been mapped out beforehand.

All we can do for now is wait till the other Fanfests to happen, as we seem to be getting the full picture in stages. The fact the trailer was partial MIGHT be the key as to how and when the full scope of the new expac will be revealed.