Why can the writers/animators use other fire moves more. Like all powerful fire type pokemons using Fire Blast or Lava Plume or Heat Wave or Eruption in the anime. They haven't even showcased Incinerate, Blast Burn, Fiery Dance in the anime yet.
As for a new fire type move for Ash's Charizard, i would really like it to learn Inferno (jp. Rengoku).
Since moves accuracy doesn't matter in the anime and anime-wise it looks more powerful than Flamethrower. Its the perfect replacement for it. And the bonus point about this move is that the flames produced by Inferno in the anime is purple/blue in colour. Plus both its japanese name and english name sound great.