I agree that the 586 may not have the sex appeal of a lugged carbon frame, but it does have other aesthetic appeal. The smooth contours and transitions from tube to tube and the (relatively) small diameter tubing gives the frame a nice classical look to it, similar to a nicely fillet-brazed steel frame. And remember, the 586 has been out for some time now (since 2008) and has remained basically unchanged since its introduction. There are several ISP frames that may look similar to the 586, but the 586 was one of the first. It wouldn't surprise me if it undergoes a change in the near future. After riding aggressive carbon frames I wanted something with a little less bite and the 586 was designed with that in mind.
For the most demanding rider, Look had the 595, but now that has been replaced with the (basically) lugless 695. So actually I think their lineup is more homologized now as there are no more lugged frames.