Saves the state money in upkeep, with the tradeoff being that the private nonprofit can set its own rules on access.
These sorts of public/private land trusts are by far the most popular way in California of ensuring wildlands are not developed and remain open for public access. It makes sense for the state to contribute to them, too, because they provide QoS guarantees - and financing largely supported through philanthropy - the state would never be able to ensure.