That was the point of the Triumphal Entry, to fulfill the prophecy that Jesus would show up on that very day.  When Israel failed to acknowledge Him properly, that meant they had to wait until God was ready to try again before they would get another opportunity to receive their Messiah.  They are still waiting for that moment, even today.  When does God say all of Israel will be saved, according to Zechariah?

-When they repent-

-When they lay aside their iniquity with mourning-

-When they turn to the God of their fathers-

-When they look on God, whom they have pierced-