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.