So whenever I explored a Cave I always compared it to that Trailer. "Does this cave enhance the gameplay?" and the answer was always no, it was just a random cave with no consideration for the gameplay, the characters abilities, or what have you.
I'm a little confused. Are you expecting that everything in the "below dirt above hell" to be meaningful gameplay beyond as a filler for exploration and travel? (I'm not sure if that capitalization is a typo or intentional because there's nothing I remember in the caves being 'noteworthy' to the degree that I'd capitalize it - as opposed to, for example, golden vault/jungle chests, or the underground wood structures, which I wouldn't describe as a cave.)
I could understand a desire to see a "Cave", a meaningful location of noteworthy consequence, which could contain items or chests or special enemies or resources or a rogue-like vault (a pre-built locked area containing "out of depth" enemies but also out of depth rewards), or perhaps even non-resource based gameplay, like the ability to create a viable house in that location that could be used for housing a few useful NPCs or as a secondary outpost. Ostensibly this sort of thing is somewhat covered by the "underground houses". But even if these were implemented, there would only be a few in any given world and the bulk of the layer would just be generic "caves", which would still fall short of your expectation that they should enhance gameplay somehow.
It may not "enhance gameplay," but sometimes a cave is just a cave. You need some kind of baseline area for the player to explore without it being all noteworthy.