You're welcome.  In the 1930s and 1940s, a competitive market for health insurance developed in many places in the United States. Typically, premiums tended to reflect risks, and insurers aggressively monitored claims to keep costs down and prevent abuses. Like before the ACA.

 Following World War II, however, the market changed radically. Hospitals had created Blue Cross in 1939, and doctors started Blue Shield at about the same time. Under pressure from hospital and physician organizations, the “Blues” won competitive advantages from state governments and special discounts from medical providers. 

Hospitals were reimbursed on a cost-plus basis.  The role of insurers was to pay the bills with few questions asked.

The philosophy of the Blues was that health insurance should cover all medical costs—even routine checkups and diagnostic procedures. Much like the ACA/Obamacare,
no deductibles and no co-payments; insurers paid the total bill.  It was prepayment for medical care