The LORD said to Moses: Speak to the priests, the sons of Aaron, and say to them: None shall defile himself for any [dead] person among his kin, except for the relatives that are closest to him: his mother, his father, his son, his daughter, and his brother; also for a virgin sister, close to him because she has not married, for her he may defile himself. But he shall not defile himself as a kinsman by marriage, and so profane himself.
I think I understand why a priest would want to stay away from a dead body. The body represents contagion. It's also spoiling in the heat.
But why is wife excluded from the list? A priest may be exalted (verse 10), but a priest is still a man and has emotions. Surely he will grieve at the death of his wife - it is a major life event. Is G-d so insensitive that he would deny the priest the opportunity to grieve at his wife's death?