My understanding is that things were incredibly homogeneous until the time in which baryonic acoustic waves started creating compressed and expanded areas. If there were black holes in that homogeneous soup, when things were so dense, it seems like everything would turn into a black hole or get sucked it.

Assuming light going into a black hole adds to its mass?

But assuming some light and matter didn't get sucked in and that's what remains, then I can understand why black holes are proposed as a possible answer to the mystery of dark matter.