Well, you've nailed it in your parenthetical comment. Lack of a credible motive is one of the telltale signs of conspiracy theories, but has never kept conspiracy nuts from presuming all kinds of nefarious motives if they fit into their preconceived world-view.

Of course the CIA could have constructed a complicated false flag operation to get Trump elected, but they lack a reasonable motive. Similar things can be said about many conspiracy theories, only few of them attribute credible motives to the state actors and/or individuals involved.