Well, maybe it's because Russian national-security state officials have studied "A Study in Assassination," which was a top-secret, early version of a CIA assassination manual written in 1953 and disclosed to the public in the 1990s.

The CIA's manual details various methods of assassination, among which is throwing a person out of a high-story building and making it look like a suicide or an accident. The manual states in part:

For secret assassination, either simple or chase, the contrived accident is the most effective technique. When successfully executed, it causes little excitement and is only casually investigated. The most efficient accident, in simple assassination, is a fall of 75 feet or more onto a hard surface.