according to the copyright office, it's different because photographers have a direct creative input into the image produced.

'The office argued that, unlike a photographer, Midjourney users have
very limited control of the final images. Photographers manipulate
framing, lighting, subject, exposure time, depth of field, composition,
and more when creating a photograph. According to USCO, “The process by
which a Midjourney user obtains an ultimate satisfactory image through
the tool is not the same as that of a human artist, writer, or
photographer… the initial prompt by a user generates four different
images based on Midjourney’s training data. While additional prompts
applied to one of these initial images can influence the subsequent
images, the process is not controlled by the user because it is not
possible to predict what Midjourney will create ahead of time.'

https://www.cartoonbrew.com/law/midjourney-ai-images-us-copyright-office-226437.html

using AI to generate art seems closer to Art Direction, rather than the creation of art itself