[niftich]

It's affected by several factors.

Survivor bias, most prominently. "To be listed, a brand or company name must remain operating, either in whole or in part, since inception."

Surviving was helped by continuity of social structures: Japan and Switzerland have seen very little external upheaval, while Germany's contemporary territory, despite unable to claim the same, has also seen a strong adherence to local institutions throughout. These companies tend to be, disproportionately, small, local affairs, so a tight-knit group of people was able to sustain them throughout generations as borders were being redrawn on the macro level.

In places where warfare and demographic change led to the movement or fall of entire populations, the continuity of such institutions was put at risk.

As a related factor, survival of documentation and the quality and continuity of recordkeeping also plays into this list.