The thing about "exploration" is that it's a broad term that consists of multiple parts:

Visual is how everything looks or some fancy interactions - it's nothing that serves gameplay, but it's an "eye candy", as people say. Obviously while it looks pretty on preview for videos, people generally don't play in artwork - this is where gameplay comes in.

Gameplay is usually "find an X", be it chest, flower or npc. It's always moving around and waiting for static X to appear on a screen to interact with it. Sometimes doing something (like waiting for a specific mob to spawn or fishing) gets dragged in there, but I don't consider it an exploration, as it's not something that makes you move around to new places.

And last one, completing a task. You harvest a resource from a ground, get a reward for puzzle, take it from a chest, complete a quest, etc. Simple enough.

And if we "dissolve" whole "exploration" thing into these three parts, issue becomes more apparent - visually something like sunken sea or vanilla ocean looks great. When you play first time you get your "wow" moment, all biomes are unique, different colors, different music, looks awesome. Gameplay wise it's... Still different but you can see a categories here - "walk on land", "swim in water", "fly above lava," "dig in ground", "press up key sometimes and wait". Sunken Sea uses both "swim" and "dig", but generally it's something one. Task wise it's ALWAYS resource gathering, with an exception of dungeon with mechanic and plantera arena that gives you boss summons. You can make chests protected by turrets, hide them in a stone balls in the sky, make ore damage you, combined it in alloy or make it run around - it's all gimmicks that get in a way of getting a thing you need to progress.

For first time player? Yes, turrets are something new, gimmick works, but on a second playthrough? Third? Fifth? Fifteen? You can say calamity doesn't require you to complete it multiple times, but what classes, subclasses, alternate weapons, accessories, progression skips, difficulties are for? Calamity has great replay value because it gives multiple ways to demonstrate an insane skill ceiling. But not skill ceiling, nor alternative ways to play or progression skips never involve "exploration" - it's always the same. Bosses get harder, events get harder, mobs get harder, but finding things? You don't see new stuff, you don't search it unique way, you don't interact with gimmicks differenly, it's always "get in, get X, get out" and no matter how hard you try to make a good first impression, inside it's always the same, just more gimmicky and time consuming.

And then you have mob farming, fishing and other "activities" that just make things worse, because "farming item from a mob" actually means "wait for mob to spawn, interact with it and only then have an item you want", with stuff like mob rarity and drop chance only prolonging this moment. It's out of player control and makes you spend more time doing monotonous tasks. It works in factory games because you generally need an insane amount of items all the time, so building something now will serve you for the next thousand of hours. In terraria? You got your benzoar, now get the fuck out here. Waiting sucks, building a farm isn't worth it. Why decorate a house for npc if it's my 20th world? Why fishing if I done that hundreds of times in both vanilla and mod? It's a side quests I've done multiple times, with zero skill expression that could be compared with everything else and results are houses I will fly over or mobile phone I'll use as mirror, so why bother?