Why do you say that media bias fact check is baseless propaganda?

edit: One of the most left leaning but highly factual news sites I go to is Fair.org. This site is almost always against the major mainstream media consensus, but backs up its claims with lots of high quality reasoning and evidence. MBFC rate it left-center and high factual reporting.

It gives Jacobin, probably one of the biggest left leaning news sites in the US, a left leaning and high factual reporting score. Jacobin calls themselves left leaning, of course. For anyone who knows history, it's right in their name. So what's the problem there?

Meanwhile, it gives all the major right wing news sites poor ratings. Fox News, Breitbart, Epoch times, etc. get an extreme right and Mixed factual reporting score.

So I understand why you would besmirch MBFC if you're some rightwinger. But, from the left, I don't understand. Reality has a left leaning bias.