All plural nouns are not female im german.

They just happen to use "die" as their definite article when they are nominative, which doubles up as the feminine article for fem. nominative. But they by no means "change" their grammatical gender. Within the german declination system, articles are very often reused for different cases. That does never change the gender of the noun.

Just like saying "der Frau" in genitiv singular does not make Frau a masculine noun, saying "die Männer" in nominative plural does not make Männer a feminine noun.