I think there's loads of reasons why:
- People come here (often) when they've just received life-changing news (a diagnosis of diabetes for them or a loved one) and just need a place to feel connected briefly before getting on with their lives.
- People post once, but then enjoy reading more than posting.
- People introduce themselves, but aren't confident with typing (for loads of reasons - English as a second language, new to the internet, don't have regular PC access etc)
- People just don't want to connect to a community. They have support, they just don't quite know how to shape that to their diabetes.
- People ask for specific advice about a particular thing, get loads of input and then, problem solved, go their merry way.
- People might have joined more than one forum and picked a different one to us.
And then all the less nice ones.
And exit poll could be interesting, but how do you know when someone has left? You can read without logging in, so do then wait X amount of time since their IP last showed up? And if they're disengaged from us after that time, would they really take a moment to fill in a survey about what turned them off?
To many of us, this site is a key part of our strategy, and we cherish it for that. But it makes it easy to take implicit rejection ("Why doesn't everyone love us?! We're the best forum EVER!!") personally, too. That fact is, pleasing all the people all the time just isn't possible and it's okay if people don't universally think we're fab - there are lots and lots of people who get a lot out of being here, whether they post or lurk.
It's good for a community to take a health-check (like this thread), but stoicism is also good - all those phrases our mothers used to hand out to soothe our feelings are still relevant: "Takes all sorts..." and so on.