Ash's Torterra...Need I say more?
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.
There's no need for fantastic, mind-blowing, strategic movesets on the animes because nobody cares much about strategy in the animes. They just want moves that look cool and provide excitement for the viewers. Heck, I'm pretty sure that all of Ash's pokemon have used more than four different moves before (and not because they learned new ones, they went back to the old ones occaisonally afterwards).
Well from what I've seen they suck so people havea reason to try to beat ash and his team