In terms of forks, I believe it was Maps.Me -> Organic Maps -> CoMaps.
So all forks of the same project. Maps.Me is not open source anymore (I think?), and CoMaps was started by a subset of the Organic Maps community that wasn't happy with the Organic Maps governance.
> What might make me switch?
Different reasons for different people, but OpenStreetMap is a great community project, for one. What I really like with those apps (I am now using CoMaps) is that they are open source, offline first and the UI is quite minimal and clean.
Organic Maps was founded by two of the Maps.Me authors (https://en.wikipedia.org/wiki/Organic_Maps#History).
With CoMaps I don't think, there are any original authors involved (?). In any case I prefer organic, the original. Donated and very grateful that this app works so well (except for search where I sometimes use another app).