It’s pretty easy why trust in media has eroded in my lifetime (I’m a 40 something). We deregulated and allowed for consolidation of ownership of print, broadcast and eventually online media.
That changed the dynamic. People will always correctly call out right wing talk radio as an example but the problems with media are more subtle as well. Broadcast news changed from a public service obligation to entertainment. If you were around in the 90s, you’ll remember how the OJ Simpson drama was a transformational event - which would not have happened in 1982. Serious journalism gave way to circus.
Our wiser predecessors learned in the 1920s and 1930s of the danger of mass media. Right wing nutcases like Father Coughlin, demagogues like Huey Long, America First, and more extreme left wing labor activists bear a strong resemblance to the characters in modern media.