Why isn't organic chemistry taught in 3D?
Organic chemistry is often taught in 3D.  There have long been 3D molecular models used in classrooms, as well as Fischer projections.  

Sometimes 2D is enough for a given situation.  Maybe curved 4-dimensional spacetime is needed for some situations, vicinity of neutron stars or black holes lets say.  

Use the simplist description that includes all the relavent concepts.