I think it really has to do with a having a noticeable line between an articulated face and simpler body for human like characters. Thanos's face was really we

I think it really has to do with a having a noticeable line between an articulated face and simpler body for human like characters. Thanos's face was really well animated. Even though it was mocap, he face felt like it was part of a living thing. When he talked, the rest of his body moved with it. I think the oversized head help give more room to transition. Contrast that to the faces from Cats. There is a clear delineation between the human face pasted onto the CGI cat body. Clu's face also looks pasted on to a body. All the de-aging tech suffers from this because they are usually pasting a CGI face over a real body, and the micromovements don't match. Whatever tech smooths out wrinkles also seems to reduce fidelity. Animatronics suffer from the same issue. Often the faces are highly articulated, but the rest of the body is just a frame covered in plastic. Worf and Gamora were both real actors in makeup, so they still had all the human micromovements. And anything that is fully animated doesn't have the same delineation.