Why weren't my illustrations accepted?

Plenty of thoughts… and I agree with Adobe. Whatever you intended to do, I would suggest you check to get a better quality for your generative AI. The overall quality of all your assets is terrible. I, however, would not agree with @Henrik Heigl: you won't need a model (property) release for all of those, as there is no relation to real people, comic style, or photorealistic. Even if those were photographs, with real models, but the same style, I would doubt that model releases would be requested.

1st: Artefacts and strange elements:

The transition from sharp to unsharp is not correct and, anyhow, you have aliasing in your sharp lines. I can't help, but the robot gives me the impression of a third arm when looking at the thumbnail.

2nd: Are they doing a handshake or holding hands?

Plenty of artefacts and illogical change from aliased lines (also a defect alone!) to highly burred elements.

I'll let the strange robot hand as freedom of art, but still, it's not great.

3rd: Plenty of artefacts and scissor hands:

4th: Plenty of artefacts and a twisted hand:

5th: Artefacts like this make this picture unusable:

There are plenty of such artefacts resulting from upscaling the asset.

6th: Those artefacts don't go together with the blurry background:

The picture in all is blurry. And has several other problems. You maybe could explain this horn growing out of the eyes of the person.