It's a great question! One thing I might suggest is human migration displacing garum, or displacing the people that had a taste for it. Between "Antiquity" and

It's a great question! One thing I might suggest is human migration displacing garum, or displacing the people that had a taste for it. Between "Antiquity" and today, you're as likely to find an immigrant population as a native one. I've been reading a lot about Roman history, and trying to answer questions like this, and many signs point to migration. The various -goths and Vandals in particular carved the Iberian peninsula (and southern France) out of the increasingly fragmented (Western) Roman Empire. According to the original sources, most of the garum in the Empire was produced in both provinces of Hispania. Considering the, uhh... "dynamism" of that place in the ensuing centuries, it sounds believable to me that garum simply fell out of favor culturally. Trade collapsed after the fall of the Western Roman Empire. So garum shipments from the Empire's largest garum-producing region simply stopped. It is true however that there are still Italian and Greek garum producers, as I mentioned, who claim to have been producing since Antiquity. Though this is 100% unverifiable, there's little reason to think it's not true. The thing about garum production is that IT IS SMELLY! Very, very smelly. Roman law actually forbade garum production within a certain distance to the city walls. And as the Western Empire began to evaporate, the production of most specialty / delicacy items (think wine, garum, honey, cheese, etc) moved to "wealthy manor homes" which -- because of the danger of the roads -- slowly became the armed fortress fiefdoms of feudal Europe. So probably it just fell out of favor as time wore on, except in a small few exceptional places.