Just pulling some numbers out of a hat, if they are paying $250/hr for legal counsel, and each of these disputes is generating one 8-hour day's worth of billable time, then Amazon is looking at $1.5 billion in legal fees to individually arbitrate each of these disputes.
I hardly think they are paying $250/hr for external counsel on each and every of those 75 000 arbitration cases. Amazon can easily justify hiring in-house counsel, and regular employees of legal department don't make $500k/year. More likely, they are going to hire a bunch of paralegals at $40/hour, and have each spend 1 hour tops on arguing each case.