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, all three axes are available for free sketching and the equations tool can operate fully.