Quick fix for armature / rig issue in Blender ($20 to provide / explain solution)

Quick fix needed on this Blender model. Issue with a custom rig created in Blender.
https://drive.google.com/file/d/1LoEbuEF8Own63fXieiqXFntlqMx-6C21/view?usp=sharing

Issue: model is not deforming with the armature after parenting the mesh to the armature (with automatic weights.

Realistic human model, all one mesh. I created the Armature with a simple bone rig just for practice with this model.
I parented the Mesh to the Armature and chose 'with Automatic Weights'
But when I try rotating the thigh, for example, the model is not deforming along with the armature. I Under the mesh's object data properties I can see that the vertex groups get created but no vertices get assigned to them. So it seems the automatic weights are not working.
Please determine root cause of why the model is not transforming along with the bones/rig after parenting With Automatic Weights.

Please message me to let me know if you have determined the true root cause and solution (not a workaround). I will award you a $20 project and then you can explain / show me the solution.