C-x and C-c make some sense as cut and copy. But C-v, C-z, C-y as paste, undo, and redo just make little sense. The first two make sense for their proximity to x and c in the QWERTY layout. y only makes sense if it happened to be unassigned.
Keyboard shortcuts will always fall into one of two categories: That makes perfect sense (usually mapping to a mnemonic like C-a for "select all"); That's totally arbitrary (C-y). It makes sense (and cua-mode offers it) to offer the opportunity to rebind the keys to the mainstream arbitrarily selected shortcuts, but it also makes sense to keep what's been used by emacs users for 40 years since that's what they're used to at this point (oh hell, I've been using it for 20 years, time has flown).