I think US "mainstream media" does have a left bias, although not necessarily very strong. (Disclosure: I consider myself probably a slightly right of center, but definitely left of Fox) Personally, I consider "mainstream media" to be the following: NYT, WaPo, USA Today, WSJ, ABC, NBC, CBS, CNN, NPR, Fox. (You could argue Time, Newsweek, Reuters, but I haven't heard of anyone reading Time/Newsweek in years, and Reuters is more news for news orgs and not directly accessed by consumers). I think when people say "mainstream media is left" they mean politically. According to [1], all of that list is left except for WSJ (center) and Fox (right), so 80% of "mainstream media" is left.

If you want to argue that people mean that more broadly, [2] gives mainly the same result, except that few become center-left.

I would certainly not call anything on the right side of middle in either of those graphics mainstream besides WSJ and Fox. (And frankly, I think it's arguable whether those two are mainstream) So for the US, anyway, it does seem credible that "mainstream media" leans left.

[1] https://www.allsides.com/media-bias/media-bias-chart

[2] https://adfontesmedia.com/static-mbc/?utm_source=HomePage_St...

That allsides chart is a bit weird. Poltico as left slanted!?! With all due respect, as a complete and utter centrist, the NYT and WaPo are hardly left of center. NYT gave very favorable to Trump, and disfavorable to Clinton coverage all through 2016.

Going a little further back, NYT sat on the NSA dragnet surveillance story (Risen and Lichtblau) in the 2004 election year when it very well could have cost G.W. Bush the election.

WaPo has been very careful to offer pro Trump editorials all along.

Neither can bring themselves to write "Trump lies".

This really shows how inadequate the right/left division is. The NYT is an establishment newspaper - they have a few “liberal” positions like tending to support gay rights or at least some access to abortion, although they’ve published plenty of op-eds from people who don’t - but those are more outliers than a trend. Get them started on classic leftie issues like worker or renter rights, taxing rich people, etc. and they’re about as left as you’d expect the average Yale legacy admission to be. The left/right divide really isn’t the best lens for this.

I put a lot of blame on unpaid internship culture: the national media tends to skew towards people from affluent families because that’s who can afford the early career steps in NYC or DC at way below cost of living.