There are actually many parts of the world where such voices are routinely positive or neutral[0]. People in more collectivist cultures often have a less-strict division between their minds and their environments and are more apt to believe in spirits and the ‘supernatural’ as an ordinary part of the world, so ‘voices in the head’ aren’t automatically viewed as a nefarious intrusion into the sanctity of one’s mind.

Modern western cultures treat such experiences as pathologies of a sick mind, so it makes sense that the voices present more negatively.

[0]: https://www.bbc.com/future/article/20250902-the-places-where...

Just a guess, but maybe it's reporting bias? Negative or evil actions might have more impetus to be understood by others than positive actions. I'd rather try and figure out why my friend suddenly started murdering the neighbours than why he's been getting his work done on time.

They do appear in some cases. The tiny angel on one shoulder to balance the demon on the other. The people who think God is talking to them directly* don't always lead a cult or hunt down heretics. But news stories focus on the darkness.

* I've met exactly one person, C, who admitted to this; C retold to me that other people from C's church give them strange looks when talking about it with them, this did not lead to any apparent introspection on the part of C.

There's a clear-cut religious answer but I'd get ostracized for mentioning religion anywhere here.