I don't think there's a particular connection between indirect enforcement mechanisms and inability to detect the crime, though:
- Structured transactions are illegal because we put a minimum on the amount of cash that has to move before government financial surveillance applies. The alternative (at least, one acceptable to the state) would be that the government knows every transaction you make[0] no matter the size. Since we don't want that, it has to be illegal to lie about the size of a transaction. Furthermore, the harder it is to get away with structuring your transactions, the more legible the financial system becomes and the easier it is to catch drug dealers.
- Pedophiles have not stopped possessing or distributing CSAM to reduce their legal liability. Actually, this argument ignores the main reason why pedophiles store and trade CSAM around in the first place: it's specifically to scare victims into silence and revictimize those who tell the cops. In fact, this is why we stopped calling it "child porn" and started calling it "child sexual abuse material" - because it is specifically material designed to sexually abuse children by way of it's mere existence.
If you're a "no touch" pedophile (they do exist!) that's still trading real CSAM around, well... Congratulations, Nobuhiro Watsuki, award-winning author of the hit samurai manga Rurouni Kenshin, you're still doing the dirty work for the full-contact pedo who recorded the damned thing.
As for drawn child porn, involving fictional characters (i.e. not CSAM), it is legal in certain jurisdictions. Notably, America, where the 1st Amendment errs on the side of creative expression[1]; and Japan, the thinking man's Epstein Island, where... I actually don't know why the fuck Japan is so weirdly tolerant of all this sick lolicon trash. Hell, Watsuki didn't even get cancelled when it came out he had 100 DVDs worth of actual CSAM.
There's an additional layer to this, though, in that for all the crimes you brought up, there's been a history of active state complicity in the crime:
- The CIA is a drug trafficking gang that happens to moonlight as a government intelligence agency
- A good chunk of elected officials and heads of state in multiple countries were compromised by notorious child trafficker Jeffrey Epstein
- The government doesn't pay taxes. I mean, obviously, they're the ones levying them.
We like to think of law enforcement as a cat-and-mouse game: criminals do a thing and law enforcement tries to hunt them down within the bounds of 4A/5A. The reality is more complicated. There are cases in which governments actively collaborate with organized crime, either because the government is corrupt as sin, or because the criminals are offering the state a way out.
[0] Fun fact: if you use Bitcoin, you're automatically opting into this.
[1] To be clear, while I agree with the American argument, you still shouldn't actually expose yourself to this kind of porn, because you're training yourself to get horny around kids. I shouldn't have to say this, but just because it's not illegal doesn't mean it's safe to use.