In the same way that some routes have Rain or Hail as their default weather conditions, it would make sense for the Hazard Zone to have Fallout trigger at the start of every battle. It makes sense, given the visible greenish haze on the overworld and the fact that humans can't safely go there without protective gear, that the conditions there would also affect pokemon in battle. When I played through this section, I was surprised it didn't already work that way.
It would likewise make sense for this to be the case in the outdoor courtyard area of Power Plant Zeta, though maybe just during the event and not when you go back after the championship, given that you can enter without the Hazard Suit at that point.
It would likewise make sense for this to be the case in the outdoor courtyard area of Power Plant Zeta, though maybe just during the event and not when you go back after the championship, given that you can enter without the Hazard Suit at that point.