This phrase comes from the casual way creators greet their audience on Facebook, especially at the start of live videos, stories and short clips. What's good is a familiar informal hello in online and spoken slang, and pairing it with Facebook makes it feel like a direct address to followers rather than a general greeting. Clips like this spread because they are short, easy to recognise and instantly set a friendly tone. Creators keep using it to open videos, react to posts and make content feel like a conversation.