The big problem with that hypothesis is that you have to explain why we see so little matter falling into these blackholes and they don't seem to: dark matter y

The big problem with that hypothesis is that you have to explain why we see so little matter falling into these blackholes and they don't seem to: dark matter you can basically pass right through and have your trajectory disrupted a little, whereas a black hole once you hit it becomes a zone of infinite attraction - i.e. a black hole passing near a star is pretty likely to setup in orbit around it because any matter that gets close enough inevitably gets sucked in. Dark matter - having finite mass and no singularity - doesn't have this problem.