Because bias has a “direction” of sort. American media won’t intentionally make a lie that makes the US looks bad because they are pro-US. As for lying to make enemies underestimate them, that’s just not how the US operate. They won’t try to make their enemy think they are weaker than they truly are because their strategy is precisely the opposite: the US spent a lot of resources on convincing the world that they are the most powerful with the deadliest weapons, that they can effectively wage war everywhere. They want their enemies to be intimidated into submission.
Because bias has a “direction” of sort. American media won’t intentionally make a lie that makes the US looks bad because they are pro-US. As for lying to make enemies underestimate them, that’s just not how the US operate. They won’t try to make their enemy think they are weaker than they truly are because their strategy is precisely the opposite: the US spent a lot of resources on convincing the world that they are the most powerful with the deadliest weapons, that they can effectively wage war everywhere. They want their enemies to be intimidated into submission.