Mendel Hirsch, the oldest son of Samson Rephael Hirsch wrote: "The Jew does not mourn that thousands of years ago the Temple was destroyed, but that it had to be destroyed. Not over the destruction, but over the causes of the destruction."
And what were the causes of the destruction?
To paraphrase Hirsch again: The Temple was destroyed because of boundless selfishness, greed for profits, misuse of power in service of their own interests on the part of those in authority and greed for lucre in all classes of the people, and the oppression of defenseless widows and orphans. And all of this bad behavior was justified by hollow trips to the Temple Mount with fatted cows and pretty prayers.
In the language of the Prophet, the people of Jerusalem did not "Seek justice, encourage the oppressed, defend the cause of the fatherless, [or] plead the case of the widow." They didn't protect the vulnerable or defend the rights of the innocent. Instead they just kept showing up on the Temple Mount, day after day, with their rams and incense. That's right: While vulnerable people went exploited and unprotected, the leaders of Jerusalem gathered on their mountaintop to pay lip service to God.
The Temple was destroyed because God grew tired of the charade. The Temple was destroyed to force the people to realize that all prayers and offerings are in vain if the law of the Torah is not kept, that the sweetest odors from sacrifices would not save the altar, the Temple, and the State, if they were permitted to take the place of the rest of God's statutes. Praising God is worthless if the law is forgotten, and the law boiled down to its essence is this: "That which is despicable to you, do not do to your fellow... the rest is commentary."
With this in mind, I close with another quote from Hirsch: "...every recurring ninth of Ab, is to pose the question to every generation: Is our present deeply imbued with the Jewish spirit, so filled with the Jewish way of thinking that it could form a worthy environment for a Temple of God to be erected in its midst?"