Even when they actually do have policies that they’re trying to apply consistently, the lack of a transparent process undermines the public’s confidence in their decisions. From outside, it all looks like a black box.
In a good legal system, decisions may be controversial, but at least the rationale is clearly laid out, and there’s a body of case law to serve as context. But when Facebook decides to de-amplify a doctored video of House Speaker Nancy Pelosi, or YouTube opts to demonetize Steven Crowder’s channel, there’s no way to check whether those decisions are consistent with the way they’ve interpreted their rules in the past, and there’s no clear, codified way to appeal those decisions.