The problem with hyperbaric treatment is there are not enough good studies to suggest it is an actual treatment for a lot of the conditions people are using it for. The FDA must approve its use as a medical treatment for it to be prescribed by doctors and the costs covered by insurance. Hyperbaric chamber therapy is expensive because it is only FDA-approved as a treatment for 14 conditions. Most users, like me, are doing it off-label which can cost $80 to $150 an hour. Personal home machines, like the one Michael Jackson slept in, run about $20,000.
The treatment was first created by Kansas City physician Orval J. Cunningham specifically for diabetes and cancer, which he believed were caused by organisms that couldn’t grow in the presence of oxygen. Based on his theories, a massive hyperbaric chamber sphere and hospital, The Cunningham Sanitarium in Cleveland, was built in 1928 and began treating patients. A few years later the project became financially unsustainable during the Great Depression and was closed permanently and the impressive metal sphere was disassembled and sold as scrap.
Cunningham had, years before opening the sanitarium, observed differences in healing of patients with Spanish Flu at different altitudes and began successfully treating patients using hyperbaric oxygen therapy, which inspired him to test the theory on other conditions. Ultimately, there were never enough studies done to prove its efficacy for most conditions and it seems unlikely today that any pharmaceutical company would pay the large costs associated with getting the treatment approved or studied for other conditions, and so the treatment remains largely unstudied for the wide variety of conditions it could potentially treat.