Ctrl-C is an idempotent operation. As long as the same objects are selected, using Ctrl-C two or more times has the same effect as just using it once.
Ctrl-X isn't like that (or at least not always); it destructively removes some objects and puts them in a clipboard. This cannot be repeated; the objects are gone. Of course, the UI may let you repeat it, but that's no longer the same operation. (But note that some user interfaces implement Ctrl-X as only marking the objects as a target for a cut operation that will only occur when the paste is executed; this marking is idempotent.)
Anyway, there is a psychology at play that once you have cut the objects or text, they are in a precarious state: they are gone from the original workspace (gasp!) and exist only inside an invisible clipboard. You do not want to do anything that would wipe out this clipboard, such as pressing Ctrl-X more times, or in general doing anything unnecessary. There is a sense of pressure to find the place to paste the objects as soon as possible, before you get distracted and forget.