[lisper]

That's not true. There have been many hypotheses advanced regarding the nature of dark matter (WIMPs, MACHOs) and the all have made experimental predictions. The problem is that none of those predictions have actually been confirmed by experiment, and we're running out of ideas. But this is not much different than the situation on the eve of the discovery of relativity and quantum mechanics at the beginning of the 20th century. So all of this is just business as usual for cutting-edge physics.

[college_physics]

Every plausible but failed hypothesis (its been half a century now?) bakes-in an intractability that may become permanent for any relavant timescale. There is still some hope as cosmological observations feel less exhausted than particle physics. But its a very awkward admission of defeat after some fairly triumphant decades last century.