Why does it take so long to get disability?

There are several reasons for this:
Social Security will tell you that they have thousands of cases to process and it takes a long time to fully develop and decide the cases. I also have a personal opinion which is that Social Security is hoping you will go back to work. Making a current decision about who is disabled and who just wants a check is often not an easy one for Social Security. the delay helps Social Security separate the truly disabled from the fakers. Unfortunately a lot of truly disabled individuals suffer from this