There's acquiring expertise and then there is acquiring recognition for expertise.
The first one requires passion, hard work and opportunity.
The 2nd one is trickier and in this day and age involves more risk. If you want to become known for expertise you have to share what you know. You also have to be approachable and willing to learn from the person you teach.
You could have two people with equal knowledge but the one people will say is the expert is the one who they feel comfortable learning from.
To give an example, without naming names, there is someone on LinkedIn who definitely knows their stuff. But they publish posts with the title "To laugh or to cry" in which they rip someone to shreds for a question from someone who is probably at the beginning of their journey. When I read their blog posts what comes across is someone who is knowledge rapped up in a love with their own cleverness. Both the wording and phraseology is designed to show the reader just how clever the author is rather than give a leg up to to the reader.
I did learn a lot from them, but it was through gritted teeth and eventually I found their tone (not the content) so repellant I just unfollowed them and stopped reading their material even though it would be in my interest to do so.
I have always found the atmosphere at SQLBits to be warm and friendly. Attended by people who are passionate to learn and the speakers are passionate to share. Many of the speakers are on Twitter and many respond to questions under the hastag #sqlfamily. The hash tag says it all.
This site has also been a friendly site. The spirit of SQLBits is inherent in this site and talking to the people at Redgate that same spirit seems to be part of the Redgate culture. That is why this site and simple-talk are the first places I go to for expertise, closely followed by blogs and Twitter posts from those people who had the guts to stand up and present at SQLBits.