It might be because that SEGA decided to make a different version of tails instead of doing the "metal" versions of each character, it's also why tails doll is mostly used for creepypasta games (If ever, but that's for sure). He also didn't return until Superstars, he only appears in Pinball Carnival Zone Act 2, he is only a enemy in his appearance. Which defeating means that you get a Medal.