The words defining various groups, whether they are ethnic, medical or whatever, change every few years because they get grubby and worn round the edges, and need thrown out and replaced. They start to be used more widely, to mean more than they did to start with, by people who are not familiar with the accurate medical meaning of, say, imbecile versus idiot (according to 19C censuses, an idiot is born an idiot, an imbecile becomes imbecilic with old age) or what exactly makes someone a cretin (congenital hypothyroidism, a severe deficiency of thyroid hormone in newborns, causing impaired neurological function, stunted growth, and physical deformities.)
The old words fall into opprobrium and are replaced by new ones - which are used until they too are replaced. It is not always easy to keep up with the latest terminology, there are so many subjects on which to be criticised if you miss the latest revision.