Because China doesn't need to kill people in the US?
Drones exist because of organized terrorist cells/groups operating in countries with either a government that is sympathetic and partly cooperative, a government that is unable to exert military force and influence on regions they no longer control, or countries that are effectively failed states.
Yemen has been a major operation center of Al-Qaeda, which culminated in the Yemen government declaring open war back in the late 2000's/early 2010's.
And obviously that's the entire "thing" with the War on Terror, the ability to argue that a country is able to ignore sovereignty of another nation that is harboring major terrorist organizations that are an active threat.
There are clear arguments and debates to be had, but when you're dealing with an organization that has taken enough territory from a state to where there is an open declaration of war, and that group has been organizing attacks and threats against you and allies the idea that using drones to target the terrorist organization is akin to declaring war on the host state kinda falls apart.
So to answer your question, unless America had a chunk of it's nation break off into an independent militant state that the Federal government is unable to control or exert force on, and that uncontrolled territory is suddenly coordinating attacks on Chinese bases, civilian populations and so forth, there wouldn't be any reason for China to start lobbing drones.
