Because nobody dies of cancer in Russia...
Korobov died "after a long and serious illness," the Defense Ministry announced on Thursday. Various sources have informed media outlets that this illness was cancer. There had also been rumors of illness circulating in Russian media in recent months.
As the news broke, however, Western media, journalists and pundits wasted no time in deciding that this explanation for Korobov's death simply could not be true. Generously, many began to offer up their own suspicions as alternative possibilities - and they pulled no punches.
While most headlines in Western media included some form of implication that not all was as it seems, true to form, the UK tabloids took things up a notch. The Sun's headline screamed "SPYMASTER DEAD" amid "suspicion he was assassinated for botching Skripal poisoning enraging Putin."
The Daily Mail also opted to immediately link Korobov's death to the poisoning of ex-spy Sergei Skripal - but added a throwback to the 2014 downing of flight MH17 in Ukraine for good measure. The lengthy headline also claimed Korobov had "collapsed following a dressing down" from Putin - a tidbit which seems to have originated as a rumor from anonymous sources, but which is now making the rounds due to its juicy, sensational nature.
It was on Twitter, however, where imaginations truly ran wild. Unconstrained by any commitment to even the most basic journalistic standards, Twitter pundits let loose.
First up, people began to notice that Korobov had been absent from the GRU military intelligence agency's centenary celebration at the beginning of this month - a sure sign, they implied, that something fishy was going on. Perhaps, many suggested, he was poisoned. Few thought to consider that perhaps Korobov was absent because he was genuinely ill - with non-poisoning-related symptoms.
Top Twitter conspiracist Louise Mensch had a different take, proffering that theory that maybe it was the United States who killed Korobov in revenge for alleged election interference during the 2016 presidential election. "Next time, don't mess with America," she tweeted, before warning her followers not to give Putin "the complement" of assuming he was responsible.
Even the supposedly restrained BBC Newsnight got in on the action, with its host John Sweeney suggesting that Korobov must have mysteriously fallen out of a window.
Perhaps the oddest theory of all, though, was that Korobov is not actually dead - and instead preparing to take on a new identity in order to circumvent US sanctions after he was placed on a sanctions list in December 2016.
A few journalists and commentators were less sensational in their Twitter coverage, noting the knee-jerk reaction of others to jump to conclusions about Korobov's death and that while official explanations shouldn't always necessarily be believed, leading liberal opposition media in Russia have reported that Korobov was indeed suffering for months with a serious illness.