Land in this context is more of a mathematical concept: yes, you can make more land, but the surface of the oblate spheroid that we call "Earth" has a finite surface area, and it's that finite supply that gives land its population-proportional value.

Even if we're willing to stretch into a third dimension, that oblate spheroid has a finite volume, and the overwhelmingly vast majority of it is inaccessible to meaningful possession/occupation; you can only dig so far down or build so far up.