There are tons of crows around my house. I feed them, I know them, they know me, but they are so hard to become friends with. They know I'm not a threat, but they are still so afraid of me. This to me is the opposite of intelligence. Otheriwse, they are probably the best parents among the birds. They little ones have such characters and the entire extended family takes care of them.
"Intelligence" may imply "not uselessly exposing yourself to danger". As long as they don't know what they could win by becoming more familiar there is no reason for them to do so. You may try to let them discover such a reason...
Humans are probably the most unpredictable beings the crows have seen.
How would they ever know you're not a threat for sure? Usually, it's hard for a human to kill another (unless with a lethal weapon and lots of intention), but it's really easy for a human to kill a bird, even recklessly or carelessly.
Note that humans in developed societies are generally much "nicer" than what we have been for thousands of years. And even so, for many individuals today, they're not different from our barbaric ancestors...
"They know I'm not a threat, but they are still so afraid of me. This to me is the opposite of intelligence."
Frankly, you don't have enough information for that conclusion.
First of all, from a bird's point of view, we are massive, clumsy and extremely powerful creatures the size of a 10-story building. If I had to live around such creatures, I would keep my distance just in case. Something that big can hurt you even without intending to do so.
Second, you don't really know if they can trust you. It is entirely possible that someone else in your neighbourhood / region fed them, gained their trust, then hurt them (or maybe "just" captured them for some time etc., an ornithologist would do). In that case, once bitten, twice shy. Most long-lived smart birds probably witnessed their kin being killed by humans; people would be expected to suffer from a bit of PTSD after that.
Third, there may be other factors at play. For example, you might smell bad to them. We generally underestimate olfactory impressions, but few of us would love to be close friends with someone who smelt strongly of, say, gasoline. Personally, I have the experience that ticks avoid me, I had just three in my entire life, approximately once in a decade, even though I go to nature fairly frequently and Czech woods are infested like hell. I must be repulsive to them.
If you have a cat or a dog, they might be smelling them off you.
