I always thought that had to do with the fact that bats aren't actually loud. Most of the Pokemon that learn Hyper Voice are either very loud (Whismur line, Politoed, etc.) or have very specific connections to sound (Chatot, Meloetta, Igglybuff line). I think the fact that they learn Screech and Supersonic demonstrates that they utilize soundwaves, I just can't really imagine Woobat or Swoobat screaming loudly. :PNow that I think about it, it cannot learn Hyper Voice neither. The Zubat family also seems to be without Hyper Voice. Are the Japanese aware of how bats operate in real life?