Why blender adds different shader nodes when converting fbx to glb?

Question

I am trying to change the shader of an fbx model to export it in glb with the glb compatible nodes.

However the output changes the principled bsdf from christensen burley to random walk, and adds a mix vertex color and color attribute node

I have attached screenshots of the changes I made to the fbx shader and the changes that blender does to the glb shader automatically after the export

Any thoughts? Thank you in advance!