Irrespective of the linked post, let me say why I (being sort-of-a senior developer) fail to communicate my expertise. In no particular order:
1. I am discouraged or forbidden from devoting time to communicating my expertise; they would rather use it. Well, often, they'd rather I did the grunt work to facilitate the use of my expertise.
2. Same, but devoting time to preparing materials which communicate my expertise.
3. A lot of my expertise is a bunch of hunches and intuitions, a "sense of smell" for things. And that's difficult to communicate.
4. My junior colleagues don't get time off their other duties to listen to "expertise sharing", when it does not immediately promote the project they're working on.
5. Many of my junior colleagues lack enough fundamentals (IMNSHO) for me to share all sorts of expertise with them. That is, to share B with them I would need to first teach them A, and knowing A is not much of an expertise; but they're inexperienced, maybe fresh out of university.
6. My expertise may only be partially or very-partially relevant to many of my colleagues; but I can't just divide the expertise up.
7. For good reasons or bad, I have trouble separating my expertise from various ethical/world-view principles, which fundamentally disagree with the way things are done where I'm at. So, such sharing is to some extent a subversive diatribe against the status quo.
8. My expertise on some matters is very partial - and what I know just underlines for me how much I _don't_ know. So, I am apprehensive to talk about what I feel I actually don't know enough about - which may just result in my appearing presumptuous and not knowledgeable enough.
9. My expertise on some matters is very partial - and what I know just underlines for me how much I _don't_ know. So, I try to polish and complete my expertise before sharing it - and that's a path you can walk endlessly, never reaching a point where you feel ready to share.
10. Tried sharing some expertise in the past, few people attended the session, I got demotivated.
11. Tried sharing some expertise in the past, few people were engaged enough to follow what I was saying, I got demotivated.
12. Shared some expertise in the past, got a positive feedback, but then those people who seemed to appreciate what I said did not implement/apply any of it, even though they could have and really should have.