Because it's the anime, there isn't as much need for type coveage. The show is made to have action and try to excite people. Game Freak doesn't keep up with the metagame, so they just use the moves that will look cool. Competitively, bullet seed is next to useless on Sceptile for Subreaking (substitute comes up so much on the anime, right), but it can still be used for some creative stuff. Likewise, the move Hyper beam is actually very useful in the anime, whereas the games where you are shunned for using Hyper beam or Giga impact on anything other than slaking.