I think it’s more a matter of, “We know there’s something that’s causing an effect, but we can’t see it or fully explain it… yet.” There’s something in the science and observations that’s just not lining up the way it should. There are some ideas that have floated around that say that dark matter isn’t necessary, it’s just a misunderstanding of one factor or another, but nobody has really been able to nail the question yet, so it persists.