The Jewish Historian Josephus, who lived from 37 to c. 100 A.D., reveals the primary reason why anyone would seek David's lost tomb and attempt to raid it. Like with many things involving humans, it all boils down to acquiring as much wealth as possible.
"He (speaking of David) also left behind him greater wealth than any other king, either of the Hebrews or, of other nations (including Alexander the Great, whom Josephus also wrote about), ever did.
"He was buried by his son Solomon, in Jerusalem, with great magnificence . . . moreover, he had great and immense wealth BURIED WITH HIM . . . (Antiquities of the Jews, Book 7, Chapter 15, Sections 2 and 3).
David, Israel's third king, is arguably the Old Testament's second most important individual (the first is Moses). A man after God's own heart (1Samuel 13:14), he was blessed to acquire a massive amount of riches for Jerusalem's temple. He collected such vast quantities of wealth, far more than needed, that an overwhelming majority of it (possibly 90%) was buried with him.
Within a short time after his death in 970 B.C., however, his tomb was forgotten. It would take more than 800 years, in a time of great suffering, for his burial location to be rediscovered . . . and plundered for its wealth!
The First Tomb Raider
The first person known to have found and raided David's burial area was John Hyrcanus. John's father was Simon Thassi (Maccabee), one of the brothers of Judas Maccabee. Hyrcanus succeeded his father as High Priest after he was assassinated in 135 B.C.
The Seleucids, soon after John became High Priest, sought to regain control of Jerusalem lost during the Maccabean revolt. Led by Antiochus Sidetes, they began a several months long siege of the city (Antiquities of the Jews, Book 13, Chapter 8, Section 1).
John, aware of the suffering from the siege, negotiated a truce with Antiochus (1906 Jewish Encyclopedia article on John Hyrcanus). Along with other concessions, he agreed to pay, immediately, 3,000 talents of silver (the Jewish Encyclopedia states 300). Hyrcanus was able to quickly lay his hands on the cash needed to buy peace by raiding the wealth in David's tomb!
"And now Antiochus was so angry at what he had suffered from Simon, that he made an expedition into Judea . . . but Hyrcanus opened the sepulcher of David . . . and took thence about three thousand talents in money, and induced Antiochus . . . to raise the siege" (Wars of the Jews, Book 1, Chapter 2, Section 5).
"He (Hyrcanus) is said to have taken this sum from the treasure in David's sepulcher" (1906 Jewish Encyclopedia).
Herod the Great Thief
The next person to seek after the lost burial location for quick wealth is Herod the Great. Aware that John Hyrcanus found treasure, and that far more still laid untouched, he discovered a second chamber near the king that John left untouched.
Although Josephus seems to partly contradict himself (compare Antiquities, Book 7, Chapter 15, Section 3 versus Book 16, Chapter 7, Section 1), it does appear Herod retrieved precious items and some money from the tomb.
"Nay, after him (John Hyrcanus) . . . Herod the king opened another room, and took away a great deal of money, and yet neither of them came at the coffins of the kings themselves . . ." (ibid., Book 7, Chapter 15, Section 3).
Herod's Second Attempt
Herod's lust and vanity knew no bounds. He tries, a second time, to find still more buried wealth even if it means raiding the chamber where both David and Solomon are laid. This time, however, his two trusted guards sent to do his dirty work are thwarted in their efforts by what seems to be a miraculous fire!
"However, he had a great desire to make a more diligent search, and to go farther in, even as far as the very bodies of David and Solomon; where two of his guards were slain by a flame that burst out upon those that went in . . ." (ibid., Book 16, Chapter 7, Section 1).
According to Josephus, Herod (who was known not to fear God or man) became so frightened by what happened that he placed an expensive white monument at the sepulcher's entrance. He then, it seems, covered up the path he used to access the burial location.
Conclusion
King David, Israel's greatest ruler, was buried with vast amounts of wealth - of gold, silver and other valuable items. After three attempts to raid his lost tomb, however, it seems to have evaded rediscovery even into modern times. Will God allow us to find it before Jesus returns? If it is ever found and excavated, will it still contain untold treasure or possibly possess priceless artifacts like a royal archive?