just say hello but not goodbye?

In YM, I notice some people would buzz me just to say hello then disappear off doing their own thing. Which is totally fine. But if that’s what you want to do then at least say goodbye too. It just seems rude not to. I mean, what’s the point? Say hello and not goodbye? That only works in real living condition, passing your coworkers, your teachers, etc where there’s eye contact and a smile to be axchanged. But in the net, you kinda expect that when someone greets you, they actually have something to say to you. When they don’t and don’t say goodbye it just seems.. I dunno, I take my eyes off work just for that? Gets annoying.

What do you think?