For a variety of reasons, people generally don't respond well to unsolicited advice. The tone and timing is just as important than the message. Right after defeating them is not the right time and text-based communication lacks tone. So you're delivering a difficult message at a bad time with barely any control over tone.
I know in your head you think you're improving the average knowledge/skill of the community, but let's be honest, it's mostly for your own benefit. Either someone accepts the critique and you feel like an enlightened teacher spreading knowledge or they don't, and you get to feel like a cool stoic who doesn't get emotional over vidya like those other guys.