There are legitimate reasons to be in those chairs that are not apparent without a full history or an x-ray machine. My wife broke her leg. Although it is "healed" in one sense of the word, she cannot stand for very long, walk very far and cannot walk very fast. In ATL that generally means you miss your flight. She does use a chair or cart to go long disances and deal with short lay-overs. Last month we had to go from MSP F-8 to B-10 in 40 minutes. We took the cart to the top of the escalator at C-23. She will often opt to walk to the top of the jetbridge to avoid jamming up the rest of the PAX. Is that a "miricle?" No. But if you want her to delay your departure from the plane, I will ask her to get the chair brought right to the aircraft door in the future.
Perhaps all of you judgemental non-medical people (I know that at least two of you will now unroll your medical credentials) should tend to getting yourselves on and off the aircraft and stop diagnosing the people around you.