[Jen's Revenge]

It is still around , it was just time for the show to have more cities. Especially since the Ranger teams after Space were there own teams and not direct continuations of one team like MMPR-Space. It would have unbelievable for unrelated teams to all be from the same city. Once they moved production to New Zealand it made no sense to really revisit Angel Grove anyway. Thats why we only see one warehouse in "Once A Ranger".