I see that too, but you don't always know the full story either.
I drove my younger brother to his doctors appointment for his foot; they still haven't decided whether they will leave it as it is with one small toe removed, (last month they removed the infected bone and just left the skin) or if they will cut the foot off below the knee. I took him to Walmart afterwards for shopping before bringing him back to his full time care facility on the foot problem, and yes this able bodied looking man was riding a cart. He had been told to keep weight off the foot, or they may need to cut it off.
He's now out of there and back home. So far, so good.
I haven't needed a cart yet, but I know when I was recovering from my surgeries, it was all I could do to put my things on the belt and reload them. I think I looked okay, I mean I was wearing a jogging outfit, but that was just because putting on real pants with a belt was too hard.
I think you need to let that one slide. You may not have all of the details.
I tend to park farther out and walk more when I do my shopping. I figure there's going to be somone that needs that spot that is near more then me.