It was partly that - but to be clear here the source of the original data is clear, so it’s not just “copying from OSM”. I’m not a lawyer, but don’t believe that:
- Looking at data in OSM.
- Verifying with an original source (with a licence valid for both OSM and OHM) that the OSM data does indeed match the original source.
- Verifying with the original adder of the data to OSM that they’re happy for it to be moved.
- Moving the data from OSM to OHM, citing the original licence as the “licence” for OHM, and also noting the path the data took to get there.
would be a violation of OSM’s licence.
Obviously, many of the same people active in OHM are also active in OSM, but the important group here is “people who just want to see their historical data on a map and don’t care in which project it resides”. There are plenty of examples where it’d be beneficial to both projects if OHM were a little bit more helpful towards both its potential data providers and data consumers. Former railways, (e.g. under new housing estates) is one; but there are others.