Originally the toolbar consisted of left-aligned tools, and a right-aligned "actions" area for things like a save button.
And some point we decided it would be better if everything in the toolbar was a tool, to remove custom styling for buttons-in-a-toolbar. To implement this we simply appended another toolbar to the actions area.
Setting up two toolbars leads to problems with things like narrow-mode calculations, as we as being just a messy API.
Instead we should allow toolgroups to specify an alignment: 'before' being on the left (in LTR) by default, and 'after' for tools that were previously in the actions area.