More Realistic Reasons

No conventional physics theory predicted the dark matter.

Even after evidence indicated that some form of dark matter comprises the overwhelming amount of all of the matter in the observable universe, no conventional physics theory could convincingly retrodict that this dark matter had to exist.

Worst of all, no conventional physics theory could tell us what we should be looking for. Hypotheses for the masses of the dark matter objects ranged from ultra-light hypothetical particles to very massive black holes.

Sometimes we think we are very advanced in our understanding of the cosmos, but the dark matter enigma should remind us that humility might be a more appropriate attitude.

The fact of the matter is: if you have no clue about the identity of most of the matter in the observable universe, even after decades of groping in the dark, then perhaps you have saddled yourself with some seriously under-performing physics theories, and it is time to think outside box.