It doesn't. Shift+Del, Ctrl+Ins,... can be done just using the right hand, while Ctrl+X/C/V uses the left hand. And sometime you may want to use two hands, which can be done in both cases by using the other Ctrl and Shift key. I actually use both kinds of shortcuts, depending on the situation.

Del and Ins are also conveniently close to the cursor navigation keys (arrows, home, end, PgUp, PgDn).

The reason I think Ctrl+X/C/V won out is that it is more convenient when using the mouse, it is also better with nonstandard keyboards where the "Ins" key is awkwardly placed, if not missing entirely.