American medical technology was still pretty limited in the late 19th and early 20th centuries. There were also relatively few factories that generated pharmacy drugs, and almost no rules on how safe they had to be for the public to use.
In some old movies you see characters selling remedies and elixirs out of their wagons or suitcases as the magical stuff that cured anything from bellyaches to cancer. Of course, they almost never worked and were usually full of stuff that actually hurt you. So the country had a shortage of reliable medicine. (Side Note: The Bayer Aspirin Company, one of the first big drugmakers, invented heroin as a pain reliever in the 1890s and it was legal to sell. Unfortunately, of course, there were serious side effects) Most vaccines had not yet been developed by this time, and so our population was continually vulnerable to epidemics, particularly measles, influenza and yellow fever.
Much of the rest of the country was underdeveloped, without much access to the large cities outside of a railroad, and almost no factories in the west at all. So often it was either too expensive or too difficult to get medical supplies to small town America.
Medical technology in terms of instruments for surgery and dental work were very primitive, and today we would scream if we saw those instruments when we went to the doctor.