There are numerous "open data" licences, many of which are totally incompatible with OSM. CC-BY 4.0 in this case isn't straightforwardly importable into OSM (yo

There are numerous "open data" licences, many of which are totally incompatible with OSM. CC-BY 4.0 in this case isn't straightforwardly importable into OSM (you need to get them to sign a waiver). So that's one reason to generate our own data, rather than using "open data" from a government.