Oddbean new post about login | logout I agree dark matter and energy are not bullshit, but science does deal in why. Even the dark matter theory contains a why component. Why does the redshift happen? Because there's matter there, even if we can't see it.
We often use the word "why" when we really mean "how". Such is the case in the questions you phrased. A model can have a metaphysical "why" component, but that is not mandatory. In fact, the most intellectually satisfactory models are most often disproved or unfalsifiable.
Yeah, the line between how and why does get awful blurry. Sometimes we keep using theories even if we know they're wrong/incomplete. We keep using quantum and relativity, even though they don't unify nicely. We await a better theory. Other times we keep using falsified theories in particular situations, i.e. video game physics engines using Newtonian gravity.
If a model is accurate enough and practical, there's no reason to stop using it. Good science is pragmatic and not just a pseudo-intelectual masturbation.