This can be competency in a different discipline, or being young and full of potential, or being personally interesting, etc.
In my experience experts will routinely and freely share their knowledge. People love talking about themselves.
If this has basically never happened to you, it's worth some self-examination. Do you make friends easily? Do you manage relationships well? Do you often find yourself in arguments? Do you have some recognized expertise or usefulness in some area?
There are many hints in your language. The "tend to be crap" anyways is a tell that you might have a sour attitude on life that turns people away. The "baffled by" indicates a lack of empathy and low ability to examine why your situation may differ from theirs. "Give me an example" is demanding. "Felt the need to impress me" views others' motives in a mercenary and petty way.
You're free to ignore this. But, consider that if you figure out why people aren't mentoring you specifically, it may also solve a bunch of related issues caused by a common thread.
(The thoughts above are based on little data, so don't take any of them personally if they're off base. The one big data point is never receiving advice - that is a sign of a problem. And, since you did want an example, when I entered business I cold emailed someone in my field how they did online work. They gave me a detailed and helpful answer, and we later became business partners. I have many stories like that.)