Russian online disinformation has predominantly been focussed on amplifying existing narratives. It almost always uses “conspiracy theories,” or other fringe false narratives, invented by elements of the target audience. The reason is simple: it is cheap and effective.
Amplifying existing narratives developed by the members of the target audience is cheaper than paying for experts to develop them.
One of best sources for a narrative that resonates with the target audience is a member of the target audience. The narrative has proven itself effective with the target already, it simply needs a signal boost to reach a wider blast radius.