Copyright protects the right to derive a return on the intentional work expended to produce art
In copyright law, units of artistic production are known as "works" because that's precisely what is required to produce them: the intentional work of one or more conscious entities, including time, physical and mental effort, and resources, both physical and financial. What copyright protects is the right to derive a return on the work expended to produce art, and to assert ownership of that work because it represents your effort and intent.
Works of art also cannot be unintentional, which is why a monkey cannot own the copyright in a photograph that it produced without knowing the outcome of its actions, but the photographer can own the copyright because they engineered the conditions in which the monkey was able to take the photograph. This is not to say that a non-human primate (or a conscious AI) couldn't produce an intentional artwork, but that's an argument for another day.
Jackson Pollock's works are art because he is not merely spilling or flicking paint at random. He has spent time, effort and resources in developing a technique which creates an effect, and rejects works which don't reflect his intention. It's irrelevant whether you or I like them.
AI advocates often point to inspiration as a form of copying, and argue that statistical AI tools are no different, but the concept of work negates this argument. When another artist is inspired to create a work of art in the style of Pollock, they must still expend time, physical effort and resources to learn similar techniques and achieve their desired effect, even if their work is less original.
Midjourney, ChatGPT et al are not conscious and cannot intentionally produce art, no matter how much work they expend. What they represent is a shortcut to the work by those who have the intent but lack either the time or resources to create it. Works created through the significant use of AI tools to imitate the style of other artists should not benefit from the protection of copyright, and the creators of those tools should compensate those artists from whose intentional work they are deriving a benefit, financial or otherwise.
There might be an argument that AI tools expend effort in the form of processing power, which is passed on to the users of the tools. However, this cost is (i) not paid by the person using the tool because it’s free; (ii) it is negligible because the cost of AI tools is insignificant in comparison to the aggregate effort of the original artists on which the AI tools draw; and (iii) it is divorced from the conscious intent of the person using the tool.