If I'm out of office they can still type the message and I'll see it later. If they can't wait and would send it to someone else if I don't immediately respond to the "hi", then they could either copy-paste it, or - even better - send it to some relevant channel that contains multiple people capable of assisting them instead of PMing it to me.
As long as it's just an "hi" you don't know what it is and have to assume it's super urgent. Once you answer, they can disclose the actual matter in its full mundanity, resting assured they have already confirmed your attention.
This affirms my hypothesis that the problem with British food is that they still have their nobility. France is the textbook example of the process - after they guillotined their nobles the good chefs that once served the elite had to offer their services to the general populace. But Britain? Only the nobles (or otherwise wealthy people) can have their servants at home prepare "a roast dinner or a beef wellington or a proper steak and ale pie", while the comments have to settle for "some fish fingers and chips in the oven".
To play the devil's advocate: this did happen during the crypto rush, when huge monetary value was assigned to nothings. If you buy into the idea that a JPEG of a monkey created by some algorithm brute-forcing KiSS can be worth a small fortune - it's not hard to see how VR "real" estate can be valuable.
"Sure, just let me finish
<this exact thing they were telling me to do and I was already doing>
"