I wonder how many times I've answered that question. On most boards, it's off topic. People don't need to have a "reason" to post at IHub.
But I do it for all the same reasons others have cited. It's educational. It's fun. It's addictive. By profession, I'm a research scholar; I enjoy researching and learning stuff.
And as someone else pointed out, many of us are retired or semi-retired. Probably that's the case with more IHubbers than you think. We're an aging population.