Because there's something quite different about her, but surely not as though you could easily give it a name.
"A capable, intelligent, and virtuous women - who is he who can find her? She is far more precious than jewels and her value is far above rubies or pearls. He can trust her, and she will enrich his life. She brings him good, not harm, all the days of her life." Proverbs 31:10-13