I don't get the point of 'self diagnosing', even less why they admit it

Why do people feel the need to specify that they self-diagnosed? If at least they were trying to sound smart why don't they lie? If what they're so desperately looking for is attention, then saying you have a professional diagnosis (which would be false) would make them more believable and give them more attention?? I am suspecting I might be autistic and I'm going to get a diagnosis eventually, but I don't go running around telling people I'm autistic and self-diagnosed???