Why does everything has to be russian - west, south, whatever?
Because the term Ukrainian/Belorussian wasn't used yet and the term Russian was prevalent (e.g. województwo ruskie - modern day Galicia, I believe?).
Vaximilian - nothing against the term Ruthenian itself, since "Rusin" is endonym of Rus people. However, using it selectively for modern day territory of Ukraine is questionable. We could argue that during EUIV timeframe it should not be applied to the territories of modern-day Russia. but the exclusions of White Russia lands is arbitrary. Basically, having an archaic Ruthenian alongside with modern Belorussian is anachronistic fallacy.
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