Yeah my point is only that it's a full DR site, not a "backup" that was left running as the article pointed out (and as a lot of commenters are insinuating).
Ah, I see. Some quick internet searching shows that from time to time (rarely), NYSE operates the Cermak site as the primary site for at least part of their operations - for up to a week at a time.
It seems to have multiple purposes - DR, customer software testing, etc.
Well, you do that to make sure it works. At one of my previous jobs, we'd switch the primary and secondary datacenters every six months just to make sure we could.