Whoever pays the cost becomes the customer, with all the incentives that entails. The point of arbitration is keeping the decision makers incentivized towards the companies in a way that judges and juries would never be.
For the choices that matter to the arbitration firm, they absolutely do. Without a customer who is willing to initiate arbitration proceedings, there are no fees to be collected.
If there is a huge upfront financial burden to the customers, the customers are much more likely to just drop the whole matter. And while the businesses would absolutely consider consumers not pursuing grievances to be a win, the arbitration firm does have an incentive to actually have there be some arbitration.
In arbitration, you do not have a judge, so there isn't subpoena power, and discovery is extremely curtailed.
https://www.gsb.stanford.edu/insights/why-binding-arbitratio...
It's simple. The optimum situation from Amazon's point of view is a system that gives almost enough justice to avoid public outcry, and no more. The most outrageous cases should get paid a modest amount, average cases should get paid a tiny amount, and no stretch cases should get paid. Amazon anticipated that by paying for the arbitration process, they'd end up with a set of pro-Amazon arbitrators and that, in itself, would keep the number of cases filed to a minimum. What they didn't anticipate was enough people angry enough to file cases even in a biased system just to mess with the company.