While the Wii is capable of some pretty cool shit when programmed usings its native programming instructions, the Wii version is based on the PS2 codepath and design, which is radically different than the tech used in current and last gen hardware for rendering not only geometry, but shader effects, and even the audio pipeline.
The games are so radically different in tech that they are built by two completely different teams. Texture maps do not match the layout of the 360/PS3 versions and neither does the geometry encoding.
The game is literally a port of the PS2 version (which was discontinued), but runs well enough on Wii when severely downgraded. If the WWE Games on Wii were programmed specifically with Wii instuctions instead of ported by lazy devs it would look and play loads better.
But alas, the Wii is powerful enough to emulate PS2 code, and thats exactly what its doing. Shitty Yukes and THQ. 2K didn't release on the Wii this time around because their devs were too inexperienced with porting their own code that they didn't have time to learn how to do things right.