All about the mindset.
When you're in a "want to critique beer" mindset, it's natural to critique other posts & threads
When you're in a "want to make a better beer" mindset, it's natural to help other brewers make better beer and find a common, community-driven best practice.
Plus, when you actually make the stuff, you appreciate the time, effort and thought that goes into it. When you just drink someone else's effort, all you can do is say why it tastes good or bad; you can't really offer the beer tips on how to be better.
Plus the mods are active, encouraging and helpful, and homebrewers in general tend to be a relaxed (DWHAHB) bunch.