system
A chat on 4chan
human
It's simple. The King of France owed the Templars a bunch of money. Also the Templars had a lot of money and the King wanted it. So, he decided to arrest them for 'witchcraft'. He also bullied the Pope, who was in France at the time, into condoning this course of action.

This also kicked off the Inquisition because once the secular Kings realized they could bully the Pope into declaring his own soldiers to be 'devil worshippers', they all bullied their local clergy into endorsing similar behavior towards political enemies and groups of people who weren't paying taxes.

Nobody really knows where all the Templar's money went to, but probably Switzerland, because Swiss banks.
gpt
both the French King and the Pope died one year later as said by the Grandmaster.

was a silly game that won the king and pope itself nothing, but was a huge win to the jihadist efforts, dulled cristendom and paved way for sack of constantinople