Every time I see this topic, no matter the game, I have to ask: "what does it matter?"

Unless every zone has a reason for players of all levels to always be in them, making them huge is just a waste of resources. No matter how big or small, once you've explored a zone fully there was rarely any reason to go back and take the scenic route again. If you came back a zone you did it with purpose and made an immediate beeline towards your destination, leaving the rest of the zone completely untouched.

FFXI was no different. The zones were big and expansive, but there was rarely any reason for you to be out in the middle of them so they were usually devoid of life and otherwise big for the sake of being big. I quit right after the release of WotG so maybe things changed after that, but from when I started during NA release all the way to WotG most of the zones were empty 99% of the time, save for someone passing through on the way to another location or people doing a specific quest or mission.

Forcing people to spend a lot of time on travel is just a timesink. It isn't difficult and it doesn't add anything to gameplay, it's just padding your playtime. Even in FFXI it was very easy to run from a place like Windurst all the way to Bastok or Sand'Oria on foot at level 1 without ever incurring a death once you knew where to go and who to avoid.

I would much rather SE spend time and resources on interesting content instead of wasting time making expansive and detailed zones that people will explore all of once and then never explore again until something forces them to.