What could cause data transfer to be ignored?

The red circled object is imported from CAD, and has a lot of loose surfaces, internal surfaces, custom normals, and is an all around horrible model that I don’t want to touch with a 10 foot pole.

But I need to texture it, so I modeled a simple boxy representation that I unwrapped and want to transfer the UV mapping on. However, the data transfer won’t stick. Even just trying to transfer a plane gets ignored.

Anyone know why this would happen?

It worked on the cube with identical data transfer settings.