You're not wrong, but why are they exhibiting hypochondria? These sorts of disorders are complex and multifaceted.
Yes, many people on these subreddits are hypochondriacs, by definition, but you can find them coalescing there, buying placebos, going to chiropractors, functional medicine doctors, naturopaths and reading sketchy journals because they've been told they're fine by doctors. However, it's blatantly obvious they are not fine, because if they were fine, they wouldn't be experiencing those symptoms. They may not be ill in the way they think they are, but they are not well.
Doctors are too ready to write off patients as worried well, but sometimes it turns out those symptoms are due to a real physical issue, and it can take years of fighting the system to find a solution. We're increasingly seeing that autoimmune, neurological, gastrointestinal, hormonal and other types of issues can cause issues across the whole body as well as directly triggering psychological disorders. Often these disorders are not even known to GPs who haven't kept up to date since leaving medical school. A patient with no history of mental health issues presents with sudden health anxiety and panic disorder out of nowhere, is it a primary mental health disorder or is there another underlying issue (psychological or physical) that's brought it on? You can't know unless you take their complaint seriously and properly investigate, but doctors are under time pressure and keen to just write it off as anxiety disorder and stick the patient on the antidepressant treadmill.
Other times, it is purely psychological or somatic, but so what? Mind and body health are intimately tied together. When one starts to deteriorate, the other often follows. Take some Zoloft and go for a walk may be a quick and convenient answer, it may even work a lot of the time, but evidently there are many, many people who find it unhelpful. Rather than looking at alternatives, some doctors will just try and say the same things over and over until the patient gives up.
Then we wonder why people give up on modern, science-based healthcare and get roped into less scientific disciplines. Modern medicine is one of the greatest achievements of human civilization, but many doctors seem to have forgotten that you're treating the patient, not the disease.