Until recently, less exposure to the bad consequences of economic policies and such that we commonly associate with capitalism. I know that's vague handwaving, sorry.
I'm not one of those "capitalism is bad!" guys, or saying that the Eastern European countries did it right, but what has happened in the West to the food industry has had some definitive downsides of its own.
The Baltic countries, Russia, Ukraine, and Central Asian countries are all aboriginal countries. They have preserved their traditional culture and all the lessons learned over many generations.
In contrast, Europe is mostly immigrants from the east, and people's conquered by the Goths and Romans who lived in slavery for hundreds of years and lost everything except the ability to just barely survive.
I'm afraid your knowledge of history is almost completely inaccurate.
The "Goths" were just a few dozens Germanic tribes who moved West and conquered territory which was already occupied by Germanic tribes. Now, before the latter Germans started pushing West so hard, ca. 500 BCE, there were Celts in a lot of these regions, but 1) current Celtic populations don't show any evidence of "Aboriginal Bread"; 2) Celts are very closely related genetically, culturally, and linguistically to both the Italic and Germanic peoples; 3)the Baltic peoples are Indo-European too. They aren't "aborigines," and certainly not culturally distinct and exemplary of some multi-millenial cultural continuity distinct from the Germans or Celts or Italians or Greeks or Albanians or Iranian or Indo-Aryans...etc. The non-Indo-European and non-Finno-Ugric Neolithic peoples of Europe disappeared under waves of IE and Finno-Ugric immigration everywhere (except possibly for the Basque).
The only non-immigrants are people who stayed very near the North shore of the Black Sea, but it's nonsense to claim that because they didn't move much in 5.5K years, they remembered how to make their ancestral bread, while no one else did. That area itself saw waves of immigrants (both IE and non-IE) and was basically part of the East-West highway, so the opposite scenario is much more likely.
Moreover, while the Romans enslaved people from various conquered populations, they did not enslave whole regions or tribes or clans or what have you. Prisoners were taken here and there, but large populations and their cultures were not lost to slavery. In addition, all those Germanic tribes and other conquered peoples _were_ most of the Roman Empire eventually. They didn't get enslaved or absorbed, nor did they conform much. They just took over.
One might also point out that the Northern and Western European diets never conformed to the Mediterranean.
I'm not one of those "capitalism is bad!" guys, or saying that the Eastern European countries did it right, but what has happened in the West to the food industry has had some definitive downsides of its own.