Because, time and time again, yesterday's conspiracy theory becomes today's well known (but mostly historical) fact. I remember perfectly well how people were ridiculed when they suggested that mass surveillance carried out by secret services was a thing. How about government tactics like GCHQ's JTRIG? Crazy tinfoil hat material for gullible people. Well, it was until 2014. Then it was proven true.
What do you think, what would people arguing the existence of Operation mockingbird or Mkultra or the true nature of the gulf of Tonkin incident be called if those were current issues & events.
Or look up the Tuskegee syphillis experiment. That abomination went on for 40 years. And hey, guess what the people who expressed serious doubts about WDMs in Iraq were called for a while.
The term conspiracy theory has been robbed of all meaning. It equals legitimate sceptics who point out reasonable flaws of official narratives with lunatics. People conspire all the time! You can't throw a surprise birthday party without conspiring. Sometimes people conspire for less benign reasons. But suggest as much about the same institutions who have been repeatedly proven guilty - and suddenly you are the perfect subject matter for patronizing articles.
"Conspiracy theorist!" is the battlecry of the aggressive conformist.
As for that article? One of the most unsubstantiated, opinionated and generally insulting pieces I've ever had the misfortune to read from anyone apparently associated with an actual university. Wouldn't read again - and may Olivers everywhere have mercy on the author's soul.