This would be my bet as to why you are getting no pins.

You spawned brf cakes to a non-nutritive mix. Coco-coir, straw, or various types of dung are used for bulk sub for cubes. Peat is used for casing layers. I would not expect the mycelium to be able to have enough nutrition from this mix to fruit, even if it did initially colonize this mix.

From your pics, it looks like there's plenty of moisture on the walls of your fruiting chamber, so I would not think that was the culprit.

Just my $.02