Or, you know, as aether.
It's a scientific theory. It's the best that we have right now to model the real world and be able to do prediction on its behavior.
Does it seems to be kept together by duct tape? Maybe.
Is it yet useful? Yep.
Will it be discarded if anything more fitting will came up? You can be sure of it.
Yeah, pretty much, which is why this adherence to dark matter seems even more puzzling: we already had a mysterious substance with nonsensical mechanical properties (perfectly solid, but has zero collision) that turned out to be completely superfluous; the actual answer was the different shape of the physical laws. Now we again have a mysterious substance with nonsensical properties (has gravitational pull, doesn't interact with normal matter in any other way) — could it be that it simply doesn't exist?
And it's not like the concept of aether itself was really all that useful for anything. The physicists wanted the light to have some mechanical medium to propagate through instead of being a thing of itself, that actual itself shaped mechanical media, not the other way around (mechanical properties arise from the E-M interaction, not the other way around), simply because all other known waves phenomena existed in mechanical media.