The most important reason why I give unsolicited advice -- is to get feedback on my own advice (what mistakes does my advice contain?)

If a person does not want to discuss my advice - they cannot give me feedback about my advice.

If I cannot get that feedback - why do I need that person in my life in the first place?

So when I give unsolicited advice -- I implicitly encourage people I do not need in my life - to disconnect from me. That frees my attention to people who are good with using advise as a tool for improvement.