Why didn't Zygarde save the world? Other than we wouldn't have a plot/boss battle? Well I've got a couple theories...
1. Zygarde's powers are mostly just to keep Xerneas and Yveltal in check, and Team Flare was just exploiting the legendaries, not having them run wild or fight each other.
2. He knew you'd do it because Arceus told him or something so he didn't bother.
3. He's a passive poke-god, so he can't judge people for what they intend to do or what they may do, only what they did. So until Lysandre actually fired the thing, Zygarde wouldn't intervene. This theory could mean that the cave-in was Zygarde's doing... possibly... but it looks pretty clear that the weapon either backfired and/or Lysandre pulled a rage-quit self-destruct.
4. He's a snake-slug. He got the memo but it's just taking him a while to get there. :)
5. There's some unknown trigger to his final form that relies on humanity or a partner or some missing fuel source, like mega-evolution. This mainly ties into Rayquaza needing fuel from meteorites and the prayers of humanity to stop thexenomorph Deoxys' meteor. Zygarde didn't have the means to achieve his complete form so he couldn't save anyone.
6. He's an order knight templar who feels that the world will be better off without 99% of humans and pokemon, finding order in stillness. Like Ashera from Fire Emblem. And there will come soft rains and the smell of the ground...
1. Zygarde's powers are mostly just to keep Xerneas and Yveltal in check, and Team Flare was just exploiting the legendaries, not having them run wild or fight each other.
2. He knew you'd do it because Arceus told him or something so he didn't bother.
3. He's a passive poke-god, so he can't judge people for what they intend to do or what they may do, only what they did. So until Lysandre actually fired the thing, Zygarde wouldn't intervene. This theory could mean that the cave-in was Zygarde's doing... possibly... but it looks pretty clear that the weapon either backfired and/or Lysandre pulled a rage-quit self-destruct.
4. He's a snake-slug. He got the memo but it's just taking him a while to get there. :)
5. There's some unknown trigger to his final form that relies on humanity or a partner or some missing fuel source, like mega-evolution. This mainly ties into Rayquaza needing fuel from meteorites and the prayers of humanity to stop the
6. He's an order knight templar who feels that the world will be better off without 99% of humans and pokemon, finding order in stillness. Like Ashera from Fire Emblem. And there will come soft rains and the smell of the ground...