I have never seen a keyboard which doesn't have a Ctrl on the right side.

Sure, but there's way more distance between Ctrl and PgUp then Ctrl+Tab (I'm taking a classic desktop keyboard in the account now). There are quite some more compact models where PgUp/Down are between the NumLock and - on the right side with the Numpad.

Not to mention you'd need to set the hand from one end of the keyboard to the middle, just to press something you'd otherwise move 1 key.

As I said, it's dumb.

Tons of laptop keyboards. Of course lots of those have no PgUp either.

It exists for ages already, though. You use the same shortcuts to cycle tabs in dialog boxes. And that goes back to at least Windows 95, if not further.

On Mac at least you can use Command Shift [ and ]. Which is the same as in the browsers.

Probably pretty nice for left handed mouse / trackpad users though.