The logic of it is that as a guest of the park they will try their best to mount a rescue if you get in trouble. If you are solo the lifeguards and rangers have no idea where to begin their search. Provided yes you can have a mishap where both divers perish or are in need of rescuing but more often one rather than both divers in trouble at the same time.
If you want to break the buddy team rule please do it somewhere else.
Hey there's the whole bay available if you don't want to follow the rules at Lobos. There's enough people who cannot follow other simple rules much less this one. How often have you seen people try to enter over the rocks, land on the beach, harass marine life and collect shells. The rangers are just trying to make sure that the divers are safe and accounted for. Pt Lobos is not just for divers, we share this park with hikers, kayakers, bird watchers and all the other people.
Remember for better or worse diving at Lobos is a privilege and can be taken away from us if we are not responsible about our actions.
[/rant]