The idea of the exclusionary principle is that it's the only way to have the right incentives for the authorities to abide by constitutional restrictions on their power. If they don't follow the rules, then they can't use their evidence in court. As a result, their internal procedures are designed to prevent that outcome. Despite the high profile cases and media coverage that makes it seem otherwise, law enforcement procedures tend to be much more restrictive than the constitution demands, because they want to avoid any doubt that their actions are legal and that their evidence is admissible. They also want to avoid edge-cases that could lead to court rulings that add to their constitutional restrictions, which will tie their hands in future cases where they might have a pressing need to exercise the full scope of their powers.
Without the exclusionary rule, you rely on the authorities following restrictions purely out of the goodness of their hearts, or only as much as the voters of the day demand. What incentive would the prosecutors and police have to limit their own authority? You can't have the fox guarding the hen house.