A: Licensing hell. Nintendo owns the rights to Mario and Link. Once the Wii U died, those costumes were legally entombed.
However, if you only care about competitive ranked matches, note that all official online servers for all platforms are dead. In that case, the "better" version is the one you can play locally with friends—and the Wii U version, with its four-player Pair Play and GamePad assist features, wins that battle hands down. tekken tag tournament 2 wii u iso better