It's weird that they haven't put much effort into touching up the overworld. Maybe they feel like it's not worth it; that that effort is better spent on "new content," as if it's a tradeoff that must be made. I certainly don't buy that they don't have the manpower to lend to it.

Maybe it's a victim of the devs pigeonholing themselves into this strict roller-coaster design the game has. They're very good at ensuring the player is a specific level at certain points in the story, and I'm going to guess that, in part, is due to how little they have to worry about rationing out experience rewards during an expansions leveling cycle during the MSQ. When there's so few sources of significant experience during a new MSQ and they're constantly ushering players along in the story, they can technically more easily fine-tune the experience players do get.

I fear they may look at adding new overworld content as something that would conflict with this design, as they would need to ensure it's worth the player's time to even do, and that means either experience, or currency, or both as rewards. Obviously, we don't really have either, if we're not counting hunt trains (which you won't be doing until level cap anyway), which I don't personally see as significant pieces of content. FATEs can be decent with exp, but they've been around, relatively unchanged, for a very long time now, and I'm frankly burned out on them.

That said, this isn't a defense of their overly-strict design. I hate it, actually. I hate that we don't have more interesting ways to navigate a zone, just because it would go outside of their very strict plan for where you can go and when. I hate that enemies wander around their leashed areas like the literal NPC's they are, instead of at least patrolling around, or even giving the impression that they're doing something. I hate that all flying enemies are prohibited from flying. There are enemies in dungeons that "fly" until they aggro you and come down to fight. Even WoW does that, and quite often. I hate that I have little to no incentive to engage with the overworld content that we do have, because it's so mind-numbingly tedious to me that I would take just about anything as a replacement at this point.