Why do people expect a universe full of randomness to be fair?

Because people believe in karma, or in a God who is just. And I think that for many people, believing that things will work out well for them in the end if they do good for others gives them some sense of control, or security. But it doesn't work that way. People do good and are hated or ridiculed for it. People do evil and are loved for it. This world doesn't make any damn sense, and many people, myself included, find it very hard to accept and cope with that.

Perhaps the people who expect the world to be fair
(I've heard of them but never met one)
don't believe in the randomness of the universe.

Or they might be immature and stuck in magical thinking.

Or they might have quite strange ideas of what is fair -
such as "it's only fair if it suits me" - a symptom of a personality disorder.

It's not so easy to generalize on a trait like this - one needs to know the individual.

I just know what I like and what I don’t.

It's an attempt to organize chaos

Because a good deal of them are raised to believe they're best mates with a 'creator' of the universe.

Because they subscribe to a right/wrong philosophy.

Humans are self-centered, I guess.

To be fair, context is important, what are you refering to exactly please.

The universe is full of everything except that.

yes. it is.