I sometimes have difficulty remembering people's names. Even people I have known for years.
It's really frustrating when you suddenly see someone you know very well and can't more than a "Hey! ...you" out only for their name to immediately pop into your head about 30 seconds after the conversation is over and you're walking away.
ADHD is a brain/neurological disorder that has a wide range of symptoms, including memory issues. I can't tell you exactly why we have trouble remembering names but I am 100% certain that it's not because you're a bad or self-centered person.
You've gotta give yourself a little grace. Living with with ADHD is hard and you can't just power through it, any more than someone missing a leg can run marathons.
I always, always, always open with "I am VERY bad with names so please forgive me if I have to ask again next time. ... no, yes, I get that you think you're bad with names too, but you don't understand." Okay, admittedly, I only think that second part.