You have to understand that TSA is (at best) a bunch of civilians that took a training course one weekend. They're not the night-vision automatic-rifle wielding CPB narcotics teams tossing flash-bangs through windows or the USCG raiding a container ship in the middle of the ocean.
One thing you have to consider here is that TSA is a fairly young agency under the umbrella of DHS, while CBP and the USCG are their own autonomous agencies. Usually when people talk about these operations, they're talking about the big FBI probe several years back that found TSA doesn't catch a lot of firearms, and other dangerous weapons.
On the other hand, when you're talking about sea ports and drugs (for example), you're talking about maybe a cargo container full of fentanyl which could be worth hundreds of millions of dollars. Usually getting something like that into a port is actually a bit easier than getting it out too, because that requires the complicity of port personnel, or someone authoritative, to accomplish. Sea ports are not generally the sort of place you can walk into and walk out of if you're not supposed to be there, so there may also be logistics companies (knowingly or otherwise) transporting it from the port inland.
If you are talking about legitimate border crossings ("ports of entry"), there was a recent seizure of a tractor trailer packed full of methamphetamine, covered up by just a few boxes of onions. If an entire tractor trailer full of methamphetamine can make it through the border, it can safely be assumed that was a small fraction of it. If there is a market, people will find a way to get that money into their pockets.
If you'd like to look at the stats yourself, they can be found here:
And here are some articles on the topic:
A couple of interesting notes:
- As reported by Washington Post in the last article, "the plurality of those who were arrested for allegedly attempting to smuggle drugs into the United States were identified either explicitly as U.S. citizens or identified as residents of the United States." This means that most of the people found to be smuggling were U.S. citizens or permanent residents.
- Illicit opioids are fairly rarely seized, according to CPB's own stats. To me that is really troubling, considering the damage they can do in the wrong hands. The vast majority of seizures are cannabis ("marijuana"), followed by illicit stimulants (cocaine then methamphetamine). Comparatively, the fentanyl seized each year was about a hundredth of the weight of seized cocaine. Either they're really good at hiding it, or they're just not trying to find it (see: #3).
- Corruption is almost a fact of life for some CBP officers (who is, interestingly, one of the only law enforcement agencies that does not require psychological evaluations). If not simple bribery, some have been caught smuggling drugs themselves
Aside/IMO: This is why we really ought to focus on the underlying societal issues that motivate people to seek out illicit drugs and/or simply end their prohibition (which would remove any profit motive from the trade). Law enforcement cannot solve these problems.