I'm a self-interested creature. I tend to stop sharing with the Internet when my expertise gets far enough to the right of the mean that the information flow becomes unidirectional, or near unidirectional.
Of all the true geniuses I have met none are "on the internet", or if they are, are passive observers. They tend to be too busy doing amazing things than writing about it. I have no doubt that each would be a "superstar blogger" if they so decided to, but I highly doubt it's ever going to happen.
In private, they share in confidence with people they trust and organizations that they work with who treat such knowledge as competitive advantage.
The thing is, once you are at the top of your field, what incentive is there to share if you are still making personal breakthroughs on a regular basis? I don't see any.
I don't mind if the information flow becomes unidirectional for a reasonable amount of time. I usually go by the duration it takes for me to fill in the background information for the underlying idea. When the value of expressing the idea exceeds the time I'm willing to spend on explaining background information, I usually do not share.
I doubt I'm alone in that.