Because no other news outlet was running the "what if" scenario that was positioned as if the Buzzfeed story is 100% true and verified. You are drowning in stupid and are begging for the floaties to come off.
1) It's not a "what if" scenario if someone reports it to be factual
2) This is what Buzzfeed wrote:
"President Donald Trump directed his longtime attorney Michael Cohen to lie to Congress about negotiations to build a Trump Tower in Moscow,
according to two federal law enforcement officials involved in an investigation of the matter."
Do you understand the bit I've emphasised actually means?
Here's another example:
"The Easter Bunny told me to do it", says man who went on a shooting spree.
The bit that is claiming to be true here is that the man definitely said this, not that the Easter Bunny was confirmed as the instigator of the crime.
Furthermore, here's CNN's article:
https://edition.cnn.com/2019/01/17/politics/buzzfeed-trump-cohen-lie-congress-moscow/index.html
article said:
President
Donald Trump personally directed his longtime former attorney
Michael Cohento lie to Congress about the Moscow Trump Tower project,
two federal law enforcement officials involved in an investigation of the matter told BuzzFeed.
To hopefully finally bring home to you how wrong you are, what you're asserting would be like someone accusing you of telling lies after you talked about the content of the Buzzfeed news article.
By all means question whether Buzzfeed is speaking the truth about its sources and what Buzzfeed asserts these sources to have told them, or say that Buzzfeed concocted a scenario (through say a bribe) to insincerely assert <content of article>, or that Buzzfeed is simply taking the word of a couple of guys without seeing any evidence for the sake of a sensationalist headline, but what you asserted is 100% bollocks.
That's just aside from your implied requirement that the press only report "100% true and verified" content, which would be a higher bar of evidence than the justice system from most developed countries require, being "beyond reasonable doubt".
Meanwhile, as far as people who have a reasonable grasp of reading comprehension are concerned, if it turns out that Buzzfeed is verified to be incorrect about the story as a whole, Buzzfeed's respectability will take a hit because they evidently should have done more before publishing such a story, because the number one thing that matters when a respectable news source publishes a story is that the news source sincerely believes it to be true (ie. not fake news). Buzzfeed's double-down implies that they believe it to be true. My guess is that the Mueller investigation does not want the focus of its investigation to be altered when it is being reviewed because they feel that the main body of evidence lies in other charges, and while there may be adequate evidence for most people to think it's reasonably likely to be true, the Mueller investigation demands a higher standard in order to ensure that they nail their suspects to the wall with overwhelming quantity and quality of evidence, far beyond any reasonable doubt.