There is no doubt that the person who threw the rock should be tracked down and prosecuted too.
But to say that SF should not be held responsible is really not right either. They knew there was a problem, and that someone would likely get hurt. Maybe the sensible thing to do would have been to stop running the ride until the problem was resolved, either by building a taller fence, stopping access to that area, or whatever.
I mean, if it looked like a wheel was coming off the ride, but it had not yet actually fallen off, that would be reasonable grounds to stop the ride. You don't wait until the wheel does fall off and then tell people the ride is down. (TTD excepted
)
I don't think it's a case of "money chasing lawyers going after the deepest pockets." 2/3rds of the total amount is punitive damages, not going to the victim. Someone could have died. The park was negligent. They should pay. And the person who threw the rock should be jailed. But just because the rock-thrower wasn't caught doesn't mean the park should be off the hook too.