I’m already working on it, you’re all actually a great help in the process!
I was referring to the surplus of mass that has been measured in the Milky Way, which has to be accounted for (in order to explain the trajectory of all celestial bodies orbiting the BH). We have coined this additional mass the term “dark matter” because it can’t be caused by the mass of the total amount of matter objects in the Milky Way (since all celestial bodies are made up of SM particles). If this can't be explained by normal matter, we're forced to divert to other explanations.
It looks like the densest form of SM matter can’t be at the center of a BH (but I haven’t considered Fermi gas yet, as pointed out by @Mordred). However, so far SM particles have been ruled out as an explanation for all the mass we measure. This means that if “something” ("stuff", SM particles) can’t be the cause of mass, it must be “nothing” (whatever that means, I don’t claim to understand the physics of “nothing”), but the point is that there’s no option c, it’s either “stuff” or “not stuff”, so if it can't be A, it has to be B.
There’s a difference between “nothing”, meaning a gap/hole in spacetime, and the vacuum in between celestial bodies. The vacuum itself has some kind of neutrality, whereas an actual hole has an attractive force, because of its negative characteristic. Once again, what is mass anyway? The Higgs, the graviton, dark matter, aren’t they all just different forms of attraction? Why would anybody argue that mass must be caused by a SM particle?