I suspect, as frequently occurs, the mainstream and sidestream
(i.e. Fox News plus the right-leaning "alternative" media) colluded to push two opposing narratives that obscure the truth in different ways. Obviously the MSM wanted to prevent skeptical inquiry into this case, while the sidestream media ensured that those who were
trying to find more information would be led down one preordained path. And the latter played no small part in making it a sideshow, like with Fox News seemingly fabricating statements from Rod Wheeler
(depending on the truth of the accusation, this reflects poorly on either Fox or Wheeler himself), the Washington Times putting out a later-retracted story
about Seth and his brother being "well known in the intelligence circles" as responsible for the DNC email leaks, Kim Dotcom's claims being widely repeated despite having no substantiation, and various other purported bombshell disclosures that never amounted to anything. Yes, the MSM was the first to report on Assange's interview, and in the process they seeded that idea of Seth being the DNC email leaker which the sidestream media proceeded to pick up; an idea that I think was pure misdirection.
Now inquiry into Seth Rich's murder is either verboten entirely or almost exclusively fixated on the theory that he leaked the DNC emails. His actual job at the DNC in voter protection, and the interesting possibility of that relating to the fraudulent 2016 primaries, has been swept under the rug.