Ostensibly because the terms are supposed to avoid making the game actively worse for other players like farming resources in a way that warps the in-game economy for regular players, or being blatantly antisocial in a way that discourages other people from playing (although it's kind of a common complaint that they're generally pretty sloppy at this and could do a much better job). Someone playing TurtleWow doesn't inherently make anything worse for the people who play on retail though, so I don't see how you can compare the two.
Ostensibly because the terms are supposed to avoid making the game actively worse for other players like farming resources in a way that warps the in-game economy for regular players, or being blatantly antisocial in a way that discourages other people from playing (although it's kind of a common complaint that they're generally pretty sloppy at this and could do a much better job). Someone playing TurtleWow doesn't inherently make anything worse for the people who play on retail though, so I don't see how you can compare the two.