They really aren't. I actually make 3d models.

The only half ass decent ai ones are ones that are basically copies of other 3d designs made from humans to the point you can barely tell them apart. Cause it's just a copy.

These ads for ai 3d models are false.

They are poor.

So part of making 3d model assets is that the mesh is wrapped in a map.
Think of a globe wrapped in paper of a map of the earth.

Doing this allows for a much lower mesh triangle. Lower poly. But it can give the impression it's higher because the wrap is from actual images and is upscaled.

So render images look high quality but the actually aren't. It's the wrap.

Here is an example. You 3d scan a chocolate Santa. In foil. All the little wrinkles in the foil and details look like they were captured. But it's not actually true. The wrap makes it look like it's a high quality mesh. But it's just a blob shape. It doesn't actually contain wrinkles or texture.

It's all just the wrap. This sort of process is great for making digital assets. It makes low poly realistic items. But it's garbage for making 3d prints.

I'm going to reply to this with another image that shows this in relation to 3d printing.