Why does Social Security turn down so many claims for disability benefits?

There is no simple answer to this question. One reason is that there is no simple way to determine whether an individual is disabled. Most people who are disabled suffer from pain. There is no way of determining whether or not another individual is in pain, much less how much pain they are in. A second reason is that Social Security over the years has been more concerned with making sure that everyone who is receiving Social Security disability benefits is "truly" disabled than with making sure that everyone who is disabled receives Social Security disability benefits. An underlying reason is that Congress has always believed that, given a chance, many people will "fake" disability in order to get benefits.