Probably because backquote is very often used by many people. In particular, people like myself who do a lot of Lisp programming. Outside Lisp, backquote is also used in sh (unless you want to give yourself RSI by using $(...)).

And this is the problem in a nutshell, there really is no single keystroke that everybody can agree is the perfect one to use. You obviously don't use backquote much, so for you, thats the perfect one. For me, Control-W is pretty good, unless of course I have to run Emacs at which time it becomes a terrible choice.