Ah, because it's convenient.
Why burden yourself, presenting counterarguments, conducting complex research processes, analyzing, constantly improving yourself, gaining new knowledge. Well, it's so lazy and difficult for someone, when you can just hang a label that you are "pro-Russian" or "Putin's agent." When the narrative imposed in Western society allows you to do that without any evidence. And who in the west needs proof nowadays? It is enough for the media or biased public opinion to label you as "pro-Russian" or "Putin's agent" without any evidence, and a person in Western countries who may simply have his own point of view, but does not fit into the imposed general narrative, that person starts to have problems; he is subjected to obstruction, his accounts are frozen, he is fired from his job, and his career is hindered.
From 2017 to 2021, the United States had such a President Trump. He was the first non-systemic US president who did not obey the so-called establishment-global capital that runs everything in the US. Trump, in his campaign speech, said that his main task in foreign policy would be to establish relations with Russia. And what happened in the end. When he became president, he was immediately accused of being a "pro-Russian presidency," an "agent and puppet of Putin." His entire presidency, all Trump has done is make excuses for this. He simply wasn't given a job to do. During Trump's presidency, the largest number of sanctions against Russia were imposed. To "wash himself" from this label (because for an American official, it matters more about the internal opinion of his country than the entire world opinion), Trump forgot about his promises. They created a commission "on Russian election interference", under the leadership of R. Mueller. CIA and FBI, saying they supposedly have some evidence. Started impeachment proceedings. Broke the life and career of Trump's veteran aide M. Flynn.
And now it turns out it was all a lie, from beginning, to end! Mueller himself confirmed it. That's it!!!