The same reason you would want a diagnosis for anything, to understand the most likely root cause of problems and work on the best way to correct or adapt for them?
The first doctor I saw was not an ADHD specialist as such, he deals with ADHD but good focus of on other things (such as anxiety and depression), and while I appreciate his review I don’t believe all of my symptoms can be explained by anxiety.
For those reasons he was happy to provide a second referral to a more specialist clinic.
If I go in more prepared regarding my childhood and they still tell me it’s more likely anxiety, then I will put more focus on managing my anxiety and hopefully that will help me.
But should it be ADHD, then I would be interested in trying medication in the hope it might help me stick with tasks/projects/chores for long enough to complete them, and maybe help with impulsiveness. As well as this I would be able to get guidance to develop techniques to manage other problems at work and at home.
I’m not trying to force a diagnosis, I’m simply trying to clarify the best way forward.