We don't "have to" in the sense that it is the right thing to do. It is just the case that our standard of living will drop because of deindustrialisation.
Instead of investing in our manufacturing industries and making them more efficient we have thrown in the towel and just based everything on cheap labour – here and abroad. That gives quick profits for the globalists but in the long term we all end up working for peanuts. Once our industrial base is gone it is too expensive to build it up again.
If we had restricted immigration and our population had been allowed to drop naturally then we would not have been led down the free market road to penury. It would not have been possible to base our economy on cheap labour. Industrial automation would have taken its place.