The commenters on the site did a good job of explaining this one. There are different parties who need access to the site. It could be forest rangers, emergency responders, utility companies, landowners, landscapers, lessees, etc. Each of them provides and maintains their own lock and key, and they don’t have to coordinate key exchanges with the other parties. I’ve seen setups like this on Palomar Mountain, albeit with somewhat fewer locks.
Even the caption gets it wrong:
Can you hold on for a fortnight? I need to find the right keys.
Well, no, the locks are “wired in series” and you only need one key. That’s the whole point.