I think it's not that they have a leftist bias here, but that they have a Marxist bias. I find I get drowned, or just mass-accused of being a liberal, for simply not being a Marxist.
The false claim that Marxism is the endpoint of "left" (and that anyone who isn't Marxist is to the right of them) is silly and makes it hard to have useful conversation even if you don't care about downvotes.
The irony is, I think I agree with more points on the Communist Manifesto (not all, mind you) than I actually agree with Marxists. I feel like Communism has devolved from Marx the same way Capitalism devolved from Adam Smith.
I am actually not fond of the free market. I think regulated markets and private property with some leniency works, but is inorganic and that society is responsible to support people harmed by it. ALL forms of resource allocation are non-ideal, but a government that owns redirection (you can't steal my food because police protect it for me, but we are all responsible for you to be able to eat whether you are a "deadbeat" or not. Ditto with all necessities and some luxuries).
So basically, I'm somewhat socialist without the goal of nationalizing small business. But if you ask many folks, I'm automatically a liberal.