Saying things like "hello" or "good morning" to colleagues the first time you talk to them in a day is in many places a social convention. If you find social conventions silly, they aren't necessarily any less real. Think of them as a protocol for communicating data with other carbon-based life forms of the human model range.
Do you say bye at the end of the day? Some people do. I think its weird but some people do it. So at what level of saturation does some silly social convention like saying hi being required before sending an additional message become the expectation vs being something some people do and some people dont?
