An interesting take, never really thought about it. Why isn't it justice?

https://firstamendment.mtsu.edu/article/star-chamber/

I'm not the right person to explain English history, secret courts, and the American revolution. Suffice to say, public courts a vital check on the power of the state by way of the court of public opinion. The real final court of appeal.

Not open, not accountable by the public, lack of juries. It's not hard to see how arbitration mostly benefits corporations and not the civilians.