I agree this is misconception that a copyright license make any
direct change to data reliability. But attribution requirement
does somewhat indirectly have an impact on it, as it legally
enforce traceability.
I know that "law" has a special corner, but therefore not always the best... law, in the end, is just a social construct, just like anything we agree on. First, we all agree (it seems to me) that provenance is valuable.
However, having something in law (or contract) effectively criminalizes if you fail to add the provenance. Is that what you really wish? Do you want to be able to legally punish people if the fail to give provenance? Honestly, that sounds a bit harsh to me... and to me, and this is a personal opinion and not an argument, I think Wikidata is more open, more inclusive than that: Wikidata offers carrots, not sticks.
Egon