It‘s similar to how some people in the company’s chat first initiate a longish back and forth of formal chit-chat before actually coming to the point of asking their question. I know full well from the first „hi“ that there will be coming a question my way at some point later but now I have to stop what I was doing and engage in an unnecessary real-time conversation to enable the other side to ask. Whereas if they just asked the question outright it would not matter if I was AFK at the time. I can simply answer asynchronous.
When I come back after lunch and find a message saying simply „hi“ from 30 minutes ago and now that person is AFK it spreads out the conversation over the whole day.
I am not saying you should drop the formalities, but there is nothing that forces you to split it up into multiple messages. Just write „Hi“ followed by the question in the same message.