Physical Security is a crucial element of InfoSec, as well as being important in it's own right, for maintaining control of physical good and premises. It seems that many organizations, however, do not have a good understanding of the various vulnerabilities in their physical security... See, for example, the continued use of pin and tumbler locks, many of which can be picked fairly easily.
An interest in physical security has long been associated with hacker culture, dating back to when the AI Lab guys at MIT would pick the locks on the doors to the computer room, so they could work on their programs during off hours. Hackers continue to be fascinated with physical security for both pragmatic reasons, and simply because researching this stuff and discovering vulnerabilities is a fun intellectual challenge.
And let's face it... who doesn't want to be on a team like the one in Sneakers, doing physical pen-testing for a living?