According to the "Dragon Mother's" speed, there is still a considerable distance from JA City.
The Evil Heart Sect has taken control of JA City's communication through the Dimensional Rift. It's not easy to open so many Dimensional Rifts at once.
It requires the consumption of thousands of tons of Rift Stones.
The Evil Heart Sect would have a substantial plot to organize this event with such resources. They wouldn't want their plan to go bankrupt easily.
Once a plan fails, not only are thousands of tons of Rift Stones wasted, but the strong ones sent here will probably lose a chance to return.
So, JA City must be in a state of isolation, unable to ask for help from the outside world, or even to send messages to the outside world.
The "Dragon Mother" coming to JA City was predestined and would not change the decision due to other matters.
The arrival of the "Dragon Mother" took the Evil Heart Sect completely by surprise.