>Zygarde is supposed to protect Earth's ecosystem Kalos is just its "HQ" where a 50% of Zygarde's cells rest in snake form while the other 50% are dispersed around the globe
>all Zygarde cells have an extraordinary good capacity for detecting anomalies, making the other cells gather in an area if it's threaten by a potential menace (like in the Alola threatened by invasive species from another dimension)
>despite this, Zygarde will only act if it's 100% necessary, otherwise he would let humans or other pokemon solve the problem, in fact humans threatened by said type of menaces can't possibly find out about Zygarde's localization without the Zygarde Cube (SM), unless they just failed and Zygarde was forced to move its ass

Is Zygarde the laziest legendary ever? I bet the motherfucker he laziest legendary ever? I bet the motherfucker was there in Hoenn and Sinnoh (maybe even in Unova too since the last time Reshiram and Zekrom fought they almost destroyed the entire region) and didn't act just because it found some humans doing the job instead. No wonder why it's not even a required capture in SM, Zygarde would just sit and watch the MC save the day if he didn't have the Zygarde Cube to spot and catch its black-green ass