All the rules of evidence ultimately stem from two goals: to discourage law enforcement officers from harassing members of the public by violating their freedoms and privacy, and to discourage law enforcement officers from unfairly or prematurely narrowing the field of suspects by focusing on the first piece of suspicious evidence they can get their hands on. (More generally: don't punish wrong guy, and do punish right guy.) But once the deterrent has failed and the evidence has been collected, you end up with a known criminal you are unable to prosecute and that's a bitter pill to swallow, especially if the criminal is very dangerous and the cops' mistake was minor. The deterrence will never be 100% effective no matter how we blindly cling to that tactic.

The ideal course of action would probably be to admit all the evidence and then prosecute both the suspect and the bad cops for their respective crimes, but that's cost-prohibitive and for minor offenses even being prosecuted in the first place is often too much punishment. So as usual we end up with the courts accruing increasingly complex justifications to strike a compromise where one is needed, but the compromise the courts manage to justify isn't always a good or sensible compromise.

The problem in our system is that, when the police break the rules and get caught, the only penalty is that the evidence is excluded. "Parallel reconstruction" lets police evade even that tiny penalty for breaking the rules of evidence.

Really, there should be some personal liability for the police when they do something illegal to catch a criminal. That change isn't going to happen.

Also, "Making and selling certain chemicals." is something that shouldn't be illegal in the first place.