It’s interesting - I shared this article with someone I know who has mentored people and they had the same feedback re: saying thank you. I guess it’s pretty common for people to ask lots of questions and get lots of advice and not say thank you?
I would add that as a Mentor I found some of the questions really quite confrontingly hard. "what should I do with my life" is really hard. "my wife is worried I have a persisting health problem" likewise. You have to know when to say "seek competent input from a trained physician"
Oftentimes, what people really needed was an active listener. But I do like a good homily. We're all playing roles here.