#BackdropCMS seems to have been forked from #Drupal.
Drupal is naturally complicated, since it is really a set of frameworks and tools for building your own CMS. So it is understandable if a derivative still retains some complexity.
#BoltCMS seems to have descended from now abandoned blogging tool #PivotX ( http://pivotx.net/ ), which itself descended from #Pivot ( pivotlog net, but the current site is likely not run by the people behind the original software ). I used both of these back in the day, and if Bolt is anywhere near as easy to use, I'd be happier with it than with Backdrop.