Why was the better job not facilitated after the Istikhara prayer, despite the urgent financial need, knowing that Istikhara brings nothing but good and does not leave a person in worldly harm?

Istikhara is a specific supplication, and among the impediments to its acceptance are: doubt and testing, a heedless heart, and haste. If a servant performs Istikhara, fulfilling the conditions for its acceptance, then what Allah chooses for him will be good, even if a person dislikes it. This is because a person's love for something does not necessarily mean it is good for them, and good may lie in what they dislike. Allah Almighty says: "But perhaps you hate a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allah knows, while you know not." So Allah manages affairs with His knowledge and wisdom. Allah Almighty says: "And if Allah were to extend [in abundance] the provision for His servants, they would transgress in the earth. But He sends down in due measure whatever He wills. Indeed, He is, concerning His servants, Acquainted and Seeing."