IMS will add a vintage race in June 2014

A post on the Sportscar Vintage Racing Association, or SVRA, website revealed that IMS will host an SVRA Vintage race in June 2014 on the newly reconfigured 2.44-mile road course. For all the history that exists about IMS, this will actually be the first ever vintage race at the speedway. But why not a vintage IndyCar race as well?