But they're there because you
can't. I remember the days of Usenet and the various news groups for help. You help a person with a question and then go on to read something else... and there's a followup question a few minutes later. And another. And another.
The people answering questions have time boxed their involvement. Here's 15 minutes, here's an answer and move on.
I've had discussions on slack that span days. But that's ok... because its people I know and trust to be mindful of my time and theirs. They ask interesting questions that make me think.
To open up the spigot to everyone asking those questions (and while they are the ones I'd be most interested in having a discussion with), would make it impossible for me to ask or find anything in the future.
And as an expert in my domain, I'd be rather annoyed at getting dozens (or I suspect hundreds Jon's case) questions asking my opinion each day. I don't have time for them. I've chosen to spend time to answer this question and have a reasonable work / life / social-site balance.