Where do posters go?

I've noticed something interesting about the aviation newsgroups: posters
tend to disappear. I don't mean the posts getting lost, I mean that certain
people will post for a while and then just stop.

The way I see it, these groups have 3 types of inhabitants: the prolific
posters, the lurk mostly but post sometimes (who I feel I am a part), and
then people who post for a while and then disappear.

For example, a year or so ago, someone by the name of Tracey was asking
about questions about the medical. It seemed that she was on some sort of
medication that may have been a problem. She posted for a good 3 or 6
months and then nothing.

Another example: When I first started lurking this group, there are a
gentleman who worked as a professor of aerospace. He kept yelling at us for
discussing aviation accidents before the NTSB reports were completed. After
a while, gone.

I could go on and on reciting examples, but you know what I'm talking about.

Do these people decide to get out of aviation? I know that nobody here
knows for sure (unless you know the person some other way) so I guess this
is more of a general wondering than anything else. (I would be really
shocked if someone posted what happened to everyone how ever posted here but
then stopped.)

I guess what got me thinking about this was that I was wondering how many
(what percentage) of people get into aviation only to leave it. I think it
happens more than most think. (And, no, I'm not talking about the
percentage who fly until they cannot pass the medical due to advanced age.
I'm talking about the people who start flying and then, months or years
later, quit.) If all these people who have stopped posting are any
indication, then the number must be quite large.