First off, you are incorrect in your belief that a VA service-connected disability rating precludes you from working. It's a very common misconception. A service-connected disability rating is simply the government reimbursing the service member because an injury or illness incurred during their military service which has an impact on their quality of life after they leave the military.
Take my own rating, for example. Prior to joining the Army, I was a competitive swimmer in high school and either walked, ran, or rode a bicycle to get where I was going. While in the Army, I was diagnosed with cancer and underwent multiple surgeries and chemotherapy. Shortly after completing chemo, I developed exercise-induced asthma. Additionally, eight years of wearing 100+ pound rucksacks and taking long walks through the woods took its toll on my feet and knees. The VA has rated me at 30% for the asthma, 10% for the cancer, and an additional 10% for either arthritis or tinnitus (I'm rated 10% for one, 0% for the other, I can't remember which is which). That rating is because my life has been negatively impacted by my military service. Can I still work? Absolutely. But, I can no longer run, swim, ride bikes, chase my daughters around the yard, go hiking, or even talk on the phone at the same time I walk down the street. Hell, I get winded just walking up stairs sometimes.
Secondly, you're judging a book by its cover. You look at them and see nothing wrong. But, you don't know what's wrong with them internally. They may have a bad case of PTSD after watching their best friend get evaporated by an IED. Or, they could be like me and have a respiratory problem and bad joints. Or, if they took off their shirts, you might see scars which would make all but the stoutest of hearts cringe. (While I was going through chemo and staying at the Fisher House, one of the other occupants was an AF F-15 mechanic who'd been crushed between two cars and pinned under the hood of one, with his back resting on the hot engine until the fire department could free him. His back was nothing but scar tissue.)