It is possible the data is biased by enforcement ability. However, the difference is huge. Last year only 0.2% of fentanyl was seized at the northern border and 98% at the southern border.
I do find it interesting that the articles almost never mention the direction the drugs were moving in …
Since we don’t have outgoing searches, it’s safe to assume that 100% of the drugs reported in this way are incoming. You’d need to look at Mexico’s and Canada’s detail to see how much we’re sending that way. (Notably, it was a point of emphasis on the Trump-Sheinbaum call where she was asking for help since so many cartel firearms enter Mexico from the US)