I mean: the independent variable is 2d and the dependent is 1d, like f(x, y), that's 3d data. By 2d I mean a pie-chart, which you _can_ display in 3d (by making a "thick pie"), but it is superfluous and detracts from the data.

I think 2d graphs are easier to graphs _are_ easier to grasp, and easier to make. Not sure tooling is the main issue, there's plenty of tools around to make 3d plots.