National Treasure was the first I'd heard of the Knights of the Templar. Why were they disbanded officially?
"Officially" the King of France wiped them out claiming they were a bunch of Satan-worshipping homosexuals.
The real reason, as has been mentioned, is that they'd gotten too powerful and wealthy. The concentration of wealth they had was really beyond belief.
For the usual reasons...sodomy, heresy, and sacrilege. The same things that endear bishops today to the liberal media.
The sober consensus is that the charges were trumped up and that money and power issues were the real motives. If some members had strayed into homosexualism and gnostic occultism, it would not be the only instance an organization of merely human men ostensibly dedicated to lofty goals fell prey to the minstrations and temptations of evil.