John Gill Commentary Esther 2:10

"Esther had not made known her people nor her kindred; for Mordecai had charged her that she should not make it known." — Esther 2:10 (ASV)

Esther had not showed her people nor her kindred
What nation or family she was of; it not being asked, she was under no obligation to declare it; and being born in Shushan, as very probable, she was taken to be a Persian:

for Mordecai had charged her that she should not show it ;
lest she should be despised and ill treated on that account; fearing, if the king knew it, he would not marry her, as Aben Ezra; or rather, as the same writer thinks, that she might keep the law of God privately, observe the sabbath