While I’m not the author of the default layout, I believe that the primary reason is precisely what you listed: to avoid accidentally typing other keys. While typing
c accidentally while pressing the arrow key may not sound disastrous, it is pretty annoying when you’re navigating a menu, and pressing
v jumps you to a completely different place. Or if you want to press
Ctrl+Right, and you accidentally end up with
Ctrl+v, that’s similarly not a good experience.
Why aren’t other keys blocked? Because typically, arrow keys are often held, while PgDn usually isn’t, for example. Accidentally holding
Ctrl+v instead of
Ctrl+Right is not something I’d wish to do.
For a default layout, safety is a big thing, and the blocked keys accomplish that quite well.