I don't believe it has to do with X country takes food more seriously. I do believe it has to do with labelling at some point, say something that is labelled from X country but is coming in from Y country. The person bringing it in from Y country will argue the label is true and that it is from X country but it just costs less in Y country. But, how can border agents guarantee that it is what the label says it is? They can't. Same thing with that prosciutto, you say it is Italian made but there is no way border agents can honestly guarantee that it is and that any possible bugs/bacteria/etc aren't in it. Also, I believe that it is the whole transport of such meat/agriculture products. Things like temperatures, packaging, labelling, etc are important when it comes to food safety. Something that is deemed unfit for human consumption may get a pass elsewhere. I'm pretty sure it is an 80% of the stuff out there is safe but 20% is unsafe so customs just tackles all 100% as unsafe to prevent mistakes.