For the most part I'd say Snozz is on the money - the mycelium could have expended a lot of it's energy just to colonise those trays and possibly didn't have enough nutrients to produce fruit.

I can see that you have deep sided trays that will trap gases, to promote fruiting you have to have good air exchange. Try to fill your trays/dishes or whatever you use to the top so you don't create a C02 pocket on top of the tray. Air emanating from an air pump below most likely won't clear that pocket of C02. A small fan in the room can help a lot to get rid of that stale air, just make sure it isn't constantly blowing directly on them. A fan set on low and oscillating is perfect, it doesn't even have to blow directly at them as long as there is air movement in the room.

All that being said it appears that there could be a few knots forming in a few areas, did anything come from that grow ?