Unless you're big cheese, too many disputes can get a company cut off. Disputes aren't free to mediate, there's a cost to handle each one.

Visa/MC can block a company, happens for lots of reasons.

The more people use chargebacks to get around black hole customer service the better, because it is difficult for companies to blacklist everyone. If they don't want to pay the mediation fee, they should provide customer service in the first place.