It could be that the bg scenery isn't actually drawn when it's covered by ground but if all that really is going on in the GPU at all times then that would be like somebody suggested a really amateurish mistake.

The technology that draws only the visible objects was invented in Finland well over 10 years ago from where it quickly spread to all genres of games especially the racing games first.

But when you really start thinking about SE in-house games there really isn't that many that would benefit from this technology except of course XIV.
Many of their games have either small spaces or pre-set camera routes. It's not entirely impossible that they honestly have let this thing slip by them...