What is the wisdom behind Salat al-Istikhara in matters whose outcomes were not satisfactory, such as marriage and work, even though the person seeking guidance performed Istikhara regarding them?

If you have sought Allah's guidance (istikhara), then what He chooses for you is best. As long as your wife is religious, which is a quality the Prophet, peace and blessings be upon him, commanded, then praise Allah and hold on to her. Overlook physical beauty and look at the perfection of her religion and character, as the Prophet, peace and blessings be upon him, said: "No believing man should hate a believing woman; if he dislikes one of her characteristics, he will be pleased with another." It is not permissible for you to look at non-mahram (definition) women, so fear Allah and lower your gaze.

Regarding the distress and anxiety at work, if you sought Allah's guidance before it, its outcome will be good. Adhere to piety and increase your istighfar (seeking forgiveness), for whoever adheres to it, "Allah will make for him a way out of every worry and every distress, and provide for him from where he does not expect."