Agriculture secondaries are pretty fast, and there are a lot of good reasons for them if you have been on a farm. People do try and bring all kinds of oddball stuff back - whole salamis, hams, etc. It seems pretty funny, especially on sandwiches, but there are a couple of good reasons.

I had two bananas confiscated in Amsterdam once, so it's not just the US. In fact, in airports in South Florida, there are (or at least used to be) signs up about not transporting backyard citrus north. There are domestic inspection stations into Florida on I-95 and into California on I-80, amongst others. So, keeping the unseen passengers out of areas is important, even though it seems stupid at the time. Ask anyone in the DC area about the recent infestations of stink bugs, or snakehead fish in the Potomac, or kudzu in the south, or zebra mussels in the Great Lakes.