I can think of a few reasons.
One, he helped deliver a major advance in nuclear capability to the US, so... gratitude.
Two, the list of national heroes, who are at the intersection of national security and Nobel-Prize-worthy intellectual achievement, who are also geniuses, is short: at the top of the list, probably Einstein and Oppenheimer. Let's put it this way, anyone else you name is likely to be the equal of Oppenheimer, not 2x smarter than him. It's not a long list.
And why might that list be important?
It's not like there's a ton of geniuses lining up to work on national security today; you could say there's a 'brain drain' problem. And, rehabilitating the reputation of one of those titanic geniuses, might be a smart thing to do at a time like this.
There's pretty much no chance you're going to get a dozen Oppenheimers; so even if you have only one in the history of your institution, you should celebrate him, if only to encourage others to follow in his footsteps.