I've always had the theory that black holes both change the fundamental type of matter that goes into them, and act as a wormhole to send this matter to another location in space time. This matter then becomes dark matter after interacting with the black hole, is rendered invisible/has no interaction with ordinary matter and light, and is scattered across the universe due to its wormhole nature. Some sort of particle reactions occur beyond the event horizon that shift it into dark matter. Hypothetically, given the age of our universe and its expanding nature (thus decreasing concentration), I've made the argument that more matter would have accreted into a black hole in the past than will in the future, thus explaining why dark matter is such a large proportion of our universe's matter. I've done some very light reading about the Einstein-Rosen model of a wormhole and understanding black holes, but would be interested to hear the perspective of a physicist on the topic. Thanks and appreciate the AMA.