U.S. arms sales to Taiwan angers the commies in China

Under the Taiwan Relations Act of 1979, the USA is committed to supplying Taiwan (Republic of China) with arms to defend itself from any mainland attack from China.

Recently the United States announced a 6.4 billion arms sales to Taiwan, which angered the commies in Beijing. That sale includes 60 Black Hawk helicopters, Patriot interceptor missiles, advanced Harpoon missiles that can be sued against land or ship targets, and two refurbished minesweepers.

Commie-led China has threatened the U.S. with sanctions. Why would Beijing be upset with the sale of defensive weapons to Taiwan if Beijing does not have any dubious plans?