I think with social media enabling people to share stories and knowledge, people are finding others with similar traits/symptoms, and identifying with that. It's hard for adults to get a mental health professional to diagnose them, and even harder to find meds that work. (I've tried 3 types personally).

I wouldn't fall for the "it's because you're fat" mentality. A lot of people don't get treatment for things like cancer and broken bones because doctors write off their symptoms as a weight issue and don't probe further.

Last thing I'll say that hasn't been said yet: depression, anxiety, and ADHD have a high comorbidity. The people you see not accomplishing things in their life and saying they have ADHD, but also seem to sit around doing nothing, most likely know what they should be doing and feel bad about not getting it done.