Because of what’s called invisible disabilitres, because they are not understood or seen by the non-handicapped. Bipolar is an example. It is limiting, but not visible to the naked eye. It’s like any prejudice, based onmisunderstanding iand generalization. A person in a wheelchair is socially accepted as due handicap privileges, and a person with, for example epilepsy is not. It’s seen as laziness to get a check for the same reason, I have epilepsy, and the benefits i received were treated as fraudulent by my peers, but after my car ancient, , which put me in a wheelchair, I became perceived as legit.