A mathematically ideal sheet of paper in a 3d-dimensional space can be addressed with both 2D coordinates, within the reference frame of the paper, and 3D coordinates, within the 3D space, but given that the paper has a location in space, 2D coordinates are sufficient to specify a point in 3D space.

You can do the same with geography. It's why generally only specify geographical coordinates with latitude and longitude, altitude is a given from those two, since you're as unlikely to be hovering in the air as you are to be immersed in bedrock.

It's not that altitude isn't important, it's that it's basically determined by latitude and longitude (and time). Cultures don't exist directly above or below each other, especially not at the national scale being discussed here, and even at the micro scale, differences within a single high rise are presumably minor compared to the same distance laterally.

Also the altitude of a given lat/long can change due to geological processes, climate processes, war, etc.

The history and geography change very little whether the bird was flying while I was sitting and looking above the monitor. This is what I meant with "meaningful way". Even though a building has storys, life on 12th floor isn't much different from life on second floor. In any case, much less different than life 20 years ago, or ten kilometers away from it. In a sci-fi story or movie we see lives really in 3D, planets wrapped in habitations and such. THERE you can and should count altitude as meaningful, but we're not really there yet.