Because honestly it is junk:
1. it slows down the system
2. it makes working with the grid difficult
Why do I see the grid where my mouse was (top of the lefy object) and not everywhere on the canvas.
No application does that besides Fusion and when you zoom in out in sketches it can get choppy.
I feel those visual effects are really not a smart idea - it might look pretty or cool but for power users
they are a real pain in the you know what I mean.
Video: https://drive.google.com/file/d/0Byzv_NlyKp_2RlVrbTI4eGVIdms/view