Yes, I can see WHY it started.  Seemed like a good thing at the time for an employer to offer an extra benefit that most of the competitors didn't, to attract better employees.

But that all changed when it became the norm rather than the exception.  And along with it came all sorts of unintended consequences.  For instance, those "volume rates" sound nice from the standpoint of those getting them, but the other side of that equation is that it drives prices up for everyone else.  That's not good on the whole.  Neither is lack of portability, lack of as many choices for employees, and lack of competition among providers.  Instead of a broad marketplace with many consumers and many providers, we have a far more limited marketplace.  The customers are effectively limited to being the Benefits Managers of companies, "shopping" just a handful of large providers.  That's not good for the ACTUAL consumers (the employees).  

Worse yet, it's terrible for cost containment and price control...