The ostensible reason for them is that "court is expensive"; if this were true, and impartial arbiters could be found, at the moment a lawsuit was required, bot

The ostensible reason for them is that "court is expensive"; if this were true, and impartial arbiters could be found, at the moment a lawsuit was required, both parties could agree to arbitration at that time: just because you are or have filed a lawsuit shouldn't suddenly mean that arbitration is more expensive or impossible. That is, there is no benefit to agreeing to it at contract inception, if it were as stated: cheaper and impartial, i.e., a better court.