DSM 5.0: Why is the equations tool not available for constraint-based sketch mode?

Equations cannot be supported in the constraint-based sketch mode. In this advanced mode, you may have noted that sketched entities and applied constraints are all contained in a 2D plane, while the equations tool requires the third axis too for 3D curves like helices, viviani's and slinky. Sketching in 3D is a separate action without a base grid and relies on available entities (origin points, surfaces) to start.

With the default setting (constraint based sketch - OFF), all three axes are available for free sketching and the equations tool can operate fully.