How can I use the blur paint brush to blur vertex paint that has been baked on?

I’ve baked a texture to my vertex colour, however the blur brush is unresponsive. I know i’ve baked it properly because my “select by face colour” works fine. The “mix” and “draw” brush are responsive but the other brushes don’t seem to be making a difference as well. I’m new to blender and even less familiar with the vertex paint mode.

I can blur vertex paint i’ve added myself, however I don’t understand why this isn’t behaving as such vertex paint. Is there maybe a different way I should bake it?