They were unable to believe the good news of Messiah.
Now when Paul got to the next town he preached in, at the synagogue of Berea, "they were more noble, for they searched the scriptures daily to see if those things were so".
Is it too good to be true that God wishes all to be saved? Is it too hard to believe that His Word will return to Him fully accomplishing all which He desires and intends? Is it possible for a person, or persons, to conceive of a better outcome than God Almighty does? Is it possible for Him to be less than perfect? Does perfect lose anything? Make mistakes? Paul wrote to Timothy (1 Tim 4:10) "..to this end we both labor and suffer reproach, because we trust in the living God, who is the Savior of all men, especially of those who believe". And Jesus Himself said, "And I, if I be lifted up from the earth" (on the cross!) "will draw all men unto me". Is it really too good to be true? Is it truly easier to believe He will lose the majority of mankind? Will consign to annihilation, or worse, forever, even those who never heard the "good news"?
"Love never fails" - 1 Corinthians 13:8. Never, fails. All, should at least "search the scriptures" to see if it is really so. But! We need go back to the original words. The King's men (and others) have had a couple of preconceived notions. What does it hurt to search the scriptures to see what is so?