So don't call it a disease. Call it a Snuffleupagus. Just don't stop treating patients affected by this particular Snuffleupagus because it doesn't meet your definition of a "disease".
We aren't morally obliged to treat people for things that aren't diseases.
You aren't morally obligated to do anything, you can go live in a hut in the plains of Montana if you want. But people with ADHD who seek treatment appreciate the efforts of the medical professionals who help them.