Why duże instead of duży?
duże is (among other) Nominative plural not-masculine-personal form of duży.
duży but -> duże buty
Nominative singular masculine -> Nominative plural not-masculine-personal
I really need to do some rote memorization of adjective forms. At least they are quite regular, right?
Why if buty comes from but (masculine) suddenly the plural form is non-masculine?
I was expecting:
Duzy but -> duzi buty
There is no masculine gender in plural, only virile (a group with at least one male) and nonvirile (everything else).