I think it's a deeper disillusionment with the economy. Anyone who isn't truly rich is coming to the conclusion that it's becoming increasingly hard to get ahead in the economy over the long term, and the measures they use for economic health are becoming increasingly divorced from this reality. Things getting mildly better for some people over the recent past don't offset people's economic realities.
It shouldn't be allowed for contracts of adhesion (take or leave it contracts for consumers). Mandatory binding arbitration should be limited to business to business negotiated contracts.