I say hi to people I know all the time.
And every time I say hi again to someone in a thread, it's usually a new day.

Which, if this were real life, and I saw the same person again the following day, I would greet them again all the same.
So naturally, I'm going to say hello! <3 Plus, greeting people is lovely, and polite. You don't have to do it if you don't want to, but I don't think it's necessarily stupid. To each their own.
Also, everybody has different views on fun.

So it's not fair to judge how much fun someone is having based on your own opinions on it. For example, I have fun by greeting people, because I like people!
So hello!