I wish that were the case, but speaking as someone who lives in the prime market for the Washington (Com)Post, it's much more complicated than that. The Washington Poat still has an overall very positive reputation in the DC metro region, and its not gullability that drives people to believe what it posts, but rather a more complex set of social pressures, legacy prestige, and trust of authoritative sources.
You might want to say that can be summed up as simply "gullability" or "confirmation bias" but it's really not. When the majority of the local elites and many of the visible social organizations have adopted a progressive worldview, going against that viewpoint becomes a for of social suicide. The region used to be more balanced, with thr Maryland DC suburbs being the realm of the Progressives and Virginia DC suburbs the realm of the Conservatives, but the massive influx of progressives spurred by the Obama administration and the fact that for youngsters and families with children Virginia was a much more appealing location to move to over DC or Maryland (due to better schools, lower taxes, and cheaper real estate) you saw a fairly sharp swerve left in the VA DC suburbs (that has also dragged the state left...). This also means that many of the social organizations, businesses (which tend to be involved in government contracting... and you've seen how heavily Obama politicized the federal bureaucracy) means that upwards social standing in the region has become more and more tied to espousing the right political viewpoints. This has percolated down to the middle class of the region, to the point where someone like me, in social circles I've been in since the 2000s have had to go from being able to espouse my very mainstream Fusionist Conservative viewpoints to having to keep my mouth shut lest I be ostracized... and even THAT wasn't enough for a group of friends I've been involved with since college in the 00s to not ostracize and stop talking with me when one of the circle decided, in their mid 30s, they were trans...
And I watched as these people, who were all trans skeptics back in college, have gone about affirming trans identity while simultaneously demonizing those eho disagree with that ideology, signaling their support for this person and trans politics in general while quitely no longer communication with me... and even before this, within that group I was the one who was consistantly told to not talk politics, to not bring up politics, as to not cause problems. Meanwhile the leftists innthe group would constantly off the cuff mention politics, espoused their hatred for capitalism, or throw out the latest hot take of the left and while they would get a quick glare from some, the "let's move on" line that invaribly came up would be directed at me, even if I'd said or done nothing.
That is the level of social pressure people experience in the region. To be willing to go against that takes more than "not being gullable" or "not confirming preexsisting biases", it takes someone who genuinely has a rock solid foundation of belief and understanding, and the emotional strength and support nessesary to be ostracized from their closest friends of decades...
Thus, people will continue to echo and believe the Washington Post... as to do otherwise will make them anathema.