I mean it’s right on their site, the fact that you can’t figure out how to find basic information on the internet says a lot about you. It’s funded in large part by ads. mediabiasfactcheck.com/funding/
There are also plenty of criticisms of the site and the methodology that are well known. For example, The Columbia Journalism Review has described MBFC reviews as subjective assessments that “leave room for human biases, or even simple inconsistencies, to creep in”
There is an obvious inherent bias given that what’s considered centre is liberal mainstream centre in the west. That’s what’s known as anchoring bias, being to the left of what’s the current mainstream in the west doesn’t make something extreme in objective sense.