The worst is when people complain about "unlikable" characters or not being able to "identify" with them. Who cares? The book wasn't written so you could make imaginary friends and has zero to do with its literary merits.
If you write to make money, and people can't identify with your characters, other things being equal, you're going to sell fewer copies.
If you write to make a point, and people can't identify with your characters, other things being equal, you're going to attract fewer readers to whom you can make your point.
Why? In both cases, because people don't like reading stuff where the characters do random things for incomprehensible reasons. That's not an interesting book. You might as well write a book about squares in a video game that move according to the output of a random number generator.
That's not to say that surprising things can't happen. They have to, or again, the book isn't interesting. But the characters have to be recognizably human to us, or it quits being a book about human characters.
How about to inform, to amuse or entertain, or to tell a story?
Or because the author feels compelled to write things, or is bored and needs something creative to do?
It seems like there could be considerable distance between "likable" and "recognizably human". Lots of complaints are around the characters being "unlikable", when they're doing completely human things that are just not nice. If an author is forced to only include friendly and likable characters, there's a pretty substantial limitation on the types of human behavior that can be covered.
Sometimes you can't use "recognizably human" characters to make the point you need to make. Peter Watts is a good example of this; not only in Blindsight but throughout his body of work, the most effective characters are typically those least recognizable as human.
Such works are typically labeled as "high-concept", and I concede they can be an acquired taste. But it's not at all true to say every story is either at heart about human relationships or worthless, else this other sort of stories would never have been common enough to need naming what distinguishes them.