Correction about Wikimedia’s licensing (I’m WMF’s Deputy GC):

Collections of simple facts are not protectable under copyright law in the US or EU, so they are not governed by the CC BY-SA 3.0 license. What is protected by CC BY-SA 3.0 is the creative work: the paragraph describing the city, the picture of the city, etc. So use of simple facts from Wikipedia - population, coordinates, etc. - is not restricted by our license.

Wikidata is licensed by our contributors under CC0 1.0, a public domain dedication which also allows reuse without restrictions.

So I think it is incorrect to say that our copyleft hinders reuse of Wikimedia’s data by other projects - the focus of our copyleft is on creative works, not data/databases.

I don’t mean to leave this comment to say anything about OSM’s policy choices; just to say that it isn’t accurate to compare our copyleft situation with OSM’s.