Why did Uriah refuse to go home to his wife while he was in Jerusalem?

Answer: His comrades were in the field

Uriah said the ark, Israel, and Judah were in tents and Joab's men camped in the open field, so he would not go home and enjoy himself.

“Uriah answered, “The ark and Israel and Judah are dwelling in tents, and my master Joab and his soldiers are camped in the open field. How can I go to my house to eat and drink and sleep with my wife? As surely as you live, and as your soul lives, I will not do such a thing!””— 2 Samuel 11:11 (BSB)