Why do you think that?
There is a common article that gets passed around where a person tried to get copyright assigned to a machine and that keeps getting denied. That is very different from "AI generated images cannot be copyrighted".
If I write a program to randomly generate an image of squares of different colors:
- I, a human, can have copyright over the program text itself as a literary work
- I, a human, can have copyright over the image output of the program