It's mainly a problem of consequences and accountability. The people who suffer unjustly from unlawful surveillance and overreach are usually unable to do anything about it, and they are assumed to be criminals anyways so nobody cares. Punishments for violating the law are nearly nonexistent for "law enforcement", so a culture of impunity is formed that cannot be easily fixed. Anybody trying to enforce the rules would run into both corrupt and noncorrupt noncompliance, just like trying to get fast food workers to follow health and safety guidelines. It's probably impossible to reform and only a wholesale teardown and replacement without keeping anyone contaminated by the existing culture has a chance.