I don't know this for sure but I wonder if that explains the "medicaid waiver". Someone with a disability (and only that individual) has access to medicaid regardless of parental earned income; so we got it for my daughter. And I thought it was weird because we're probably not going to need to use it? I'm not really sure yet...I know I have good insurance but don't think have tested its limits.
And that's when I realized why they don't factor in parental income or the presence of existing insurance. It's not to cover insurance gaps if I move jobs. It's because people with disabilities will probably hit insurance maximums, and at the end of the day, you do not want guardians foregoing necessary medical care when that happens. Because it will happen. You will create a population of disabled and neglected disabled people. And I think it's the same for parks. Some people won't even try going if they think they'll lose $30.
And I know someone reading this will immediately say regular people are also being neglected. I think everyone should have access to the same care, but from a budgeting standpoint and no lawmakers wanting to appear uncompassionate, this is an easier pill to swallow. Probably why the parks page linked also mentions veterans.