...basically because coffee houses brought people together and caused people to talk. This caused them to think and question things. They questioned the kings power and he thought they were conspiring against him. Doesn't this remind you of cannabis prohibition?
He knew what he was talking about because, in America, some 100 years later, the Taverns were used as informal headquarters by many Patriot organizations during the War of Independence. Of course, banning drinking establishments didn't occur for another 150 years.