Why didn't Shu maintain its development from the north to India during the Three Kingdoms period?

In order to lay the foundation of South China, we need local indigenous autonomy. That area is full of impenetrable rainforests, endless mountains and all kinds of poisonous insects, which are not suitable for the life of the Central Plains people who farm land. Even if immigrants reclaim farmland, the cost is extremely high. Shu's national strength is not strong. How does it develop there?