TL;DR -- Why are there no Tunnel, Cave or Crypt like zones in the game yet? (Not dungeons!)

First of all I really like the zones in Stormblood. The difference in how the landscape looks and changes in the Fringes as well as Azim Steppes is really nice -- that not the whole zone looks the same, that is. So I am not picking on existing content; just to be clear. :3

So, the FF games have always been there at some point in my life. Especially so with FFXI and how it blew my mind with such vast and different areas to explore, which I have many fond memories of. There are however some zones I'd like to highlight a little extra in this post. -- Now the examples might not mean much for those that have not played FFXI but I'll elaborate further down.
Gustav Tunnel which connected Altepa Desert (it was Altepa, wasn't it? hehe) and Valkurm Dunes. All the nasty skellies down there just asking to be hit with some blunt weapons. :D