https://gcn.com/articles/2017/07/17/frederickcity-map.aspx
https://www.mapfrederick.city/about.html
https://www.cityoffrederick.com/274/Technology
No idea. Have you told them about it?
I think the MapFrederick project is solving a different issue than OSM addresses. OSM could be used for the selection box background instead of Google maps, but the detailed GIS data such as parcels, underground utilities that users could query will probably never be in OSM.