They know the media is the most powerful weapon, that's why the Elites have kept such a tight grip on it (and are still trying to control it with censorship).
Btw it wasn't only Serbs manipulated by propaganda, but also Kosovan and Albanians.
Western intelligence agencies played classic divide & conquer in the Balkans.
And seems it is actually you in Kosovo that have been kept in the dark about the real nature of the war. It is now admitted the CIA & Western intelligence supported the KLA with the purpose to start a rebellion and break up Yugoslavia. Even NATO generals over the years admitted most of the violence was initiated by the KLA, and more evidence of their brutality emerged in the recent organ harvest trials. Of course we only find out about these things once the war is over. If the Western public had know this before they would have not supported the war against Serbia.
Also the Red Cross numbers show most of the displaced in Kosovo were infact ethnic serbs, which undermines the whole "albanian ethnic cleansing" narrative. And still today we keep seeing serbs forced and intimidated to leave Kosovo.
The good thing is that now thanks to social media there are self funded citizen journalists, and the media is not controlled solely by powerful interests anymore.