VertexWeightEdit is being stubborn

I have a vertex group (“ThicknessAmt in image below”) where all my vertices are zero by default.

I want to modify those weights using a texture. I’m using the VertexWeightEdit operator on my mesh object. It’s all set up, but my weights aren’t being affected by the VertexWeightEdit operator.
Attached is an image of my setup- what am I doing wrong?
Is it my texture?
Is it the VertexWeightEdit operator?