I've wondered if the subconscious reason for sending "hi" / disliking receiving "hi" is that -- in the same way as a read receipt -- it denies the recipient the chance to read the message and tactfully choose to ignore it for some time.

E.g. no-one likes being saddled with urgent work; therefore pretending you haven't yet seen a request for such until you feel like dealing with it may be a common response; therefore asking "hi" is an attempt to establish real-time communication and thus force an immediate response to a potentially unpalatable request.