Yeah, or perhaps legalities. BTW, Edgewood is a San Mateo county park.
Based upon my experience in the park, there has been very slight ranger presence for a long time now. If there were some incident in a "closed" park as opposed to an "open" park with very spotty coverage, it might make a difference for the park district in court.
I think that closing is extreme. A warning should be sufficient, but it's a commentary on our times.
Hopefully this means that the park district is concentrating their efforts, and that we'll see more rangers (in their educational and interpretive role) on the days that the park is officially "open".
Matt