Note that Keith could have got his answer minutes sooner, and needn't have kept Tim waiting. In fact, Tim could have started thinking about the question right away!
People who do this are generally trying to be polite by not jumping right into the request — and that's great! But chat is asynchronous by nature. Despite best intentions, you're actually just making the other person wait for you to phrase your question, which is lost productivity (and kinda annoying).
The same goes for:
If it feels too abrupt to skip the greeting, you can still include pleasantries — just put them in the same message as your actual question. It also enables async communication: if someone's away and you leave before they're back, they can still answer — rather than staring at a "Hello" wondering what they missed.
When done right — everyone's happy! 🎉
You typed "hello"... the very thing this site is against. The irony is immense.