Es más rico que nadie en la ciudad.

English Translation

He is richer than anybody else in town.

Por qué no se puede decir “nadie en el pueblo?”

English Translation

He is richer than anybody else in town.

Why can’t we say “nadie en el pueblo?”

Every cloze has only one official “correct” answer, even though there are other equally valid possibilities. That’s just how it works around here. Some clozes have “alternative answers”, but given that the article is feminine, pueblo wouldn’t work here.