Georgist thinking, as far as I understand, is that taxing total property value disincentivises investment in a way that is worse for society overall. Empty land is just a subcase of that.

That said, "everybody works but the vacant lot" is a Georgist slogan that has been seen on billboards before now: https://digitalcollections.nypl.org/items/510d47de-036a-a3d9...